diff --git a/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/Errors.cs b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/Errors.cs
new file mode 100644
index 000000000000..426db3f9f569
--- /dev/null
+++ b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/Errors.cs
@@ -0,0 +1,16 @@
+using Bit.Core.AdminConsole.Utilities.v2;
+
+namespace Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.OrganizationUserAction;
+
+/// <summary>
+/// Returned when an acting user attempts to act on (or assign) an organization role that outranks their own.
+/// </summary>
+public record CannotManageHigherRoleError()
+    : BadRequestError("You cannot perform this action on a member with a higher organization role than your own.");
+
+/// <summary>
+/// Returned when the acting user has no authority to manage members for the action — for example a regular
+/// User, or a Custom user without the required permission.
+/// </summary>
+public record MissingManagePermissionError()
+    : BadRequestError("You do not have permission to manage organization members.");
diff --git a/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionRequest.cs b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionRequest.cs
new file mode 100644
index 000000000000..4e344650ef87
--- /dev/null
+++ b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionRequest.cs
@@ -0,0 +1,31 @@
+using Bit.Core.Enums;
+using Bit.Core.Models.Data;
+
+namespace Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.OrganizationUserAction;
+
+/// <summary>
+/// Whether an acting user may manage organization members at all, independent of any target.
+/// <see cref="OrganizationUserActionRequest"/> adds a target role for the full role-escalation check.
+/// </summary>
+/// <param name="ActingUserRole">The acting user's role, or <c>null</c> if not a confirmed member (they may still be authorized via <paramref name="IsProviderUserForOrg"/>).</param>
+/// <param name="ActingUserPermissions">The acting user's custom permissions. Only consulted for Custom users.</param>
+/// <param name="PermissionPicker">Picks the permission that authorizes a Custom user for this action (e.g. <c>p =&gt; p.ManageUsers</c>). Only consulted for Custom users.</param>
+/// <param name="IsProviderUserForOrg">Whether the acting user is a provider user for the org, which grants Owner-level authority. Invoked last because it hits the database.</param>
+public record OrganizationUserManageMembersRequest(
+    OrganizationUserType? ActingUserRole,
+    Permissions? ActingUserPermissions,
+    Func<Permissions, bool> PermissionPicker,
+    Func<Task<bool>> IsProviderUserForOrg);
+
+/// <summary>
+/// Extends <see cref="OrganizationUserManageMembersRequest"/> (see it for the acting-user fields) with the
+/// target role, to decide whether the acting user may manage (or assign) that role without escalating privileges.
+/// </summary>
+/// <param name="TargetUserRole">The role being acted upon — an existing member's current role, or the new role being assigned.</param>
+public record OrganizationUserActionRequest(
+    OrganizationUserType? ActingUserRole,
+    Permissions? ActingUserPermissions,
+    Func<Permissions, bool> PermissionPicker,
+    Func<Task<bool>> IsProviderUserForOrg,
+    OrganizationUserType TargetUserRole)
+    : OrganizationUserManageMembersRequest(ActingUserRole, ActingUserPermissions, PermissionPicker, IsProviderUserForOrg);
diff --git a/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidator.cs b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidator.cs
new file mode 100644
index 000000000000..69547cacfa06
--- /dev/null
+++ b/src/Core/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidator.cs
@@ -0,0 +1,81 @@
+using Bit.Core.AdminConsole.Utilities.v2.Validation;
+using Bit.Core.Enums;
+using static Bit.Core.AdminConsole.Utilities.v2.Validation.ValidationResultHelpers;
+
+namespace Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.OrganizationUserAction;
+
+/// <summary>
+/// Validates that an acting user is permitted to manage a target member without escalating privileges,
+/// according to Bitwarden's organization role hierarchy:
+/// <list type="bullet">
+/// <item>Owners (and provider users) can manage Owners, Admins, or Users.</item>
+/// <item>Admins can manage Admins or Users.</item>
+/// <item>Custom users can manage Users and other Custom users, but only when they hold the manage permission required for the action.</item>
+/// <item>All other members (including regular Users) cannot manage any member.</item>
+/// </list>
+/// A role can only be raised to a level the acting user already holds (e.g. only an Owner can grant the
+/// Owner role).
+/// </summary>
+public static class OrganizationUserActionValidator
+{
+    /// <summary>
+    /// Validates whether the acting user can manage members at all, independent of any target. Use this where
+    /// authorization needs the gate without a specific target. Returns valid, or a <see cref="MissingManagePermissionError"/>.
+    /// </summary>
+    public static async Task<ValidationResult<OrganizationUserManageMembersRequest>> ValidateCanManageMembersAsync(OrganizationUserManageMembersRequest request)
+    {
+        var isProvider = !IsAuthorizedByRole(request) && await request.IsProviderUserForOrg();
+
+        return IsAuthorizedByRole(request) || isProvider
+            ? Valid(request)
+            : Invalid(request, new MissingManagePermissionError());
+    }
+
+    /// <summary>
+    /// Validates whether the acting user may manage (or assign) the target role: the management-authority gate
+    /// first, then role escalation. Returns valid, a <see cref="MissingManagePermissionError"/> if they cannot
+    /// manage members at all, or a <see cref="CannotManageHigherRoleError"/> if the target role outranks their authority.
+    /// </summary>
+    /// <remarks>
+    /// Covers management authority and role escalation only. Callers remain responsible for other checks such as
+    /// self-actions, system/automated users, and confirmed-owner counts.
+    /// </remarks>
+    public static async Task<ValidationResult<OrganizationUserActionRequest>> ValidateAsync(OrganizationUserActionRequest request)
+    {
+        // First, the management-authority gate (shared with authorization).
+        var canManageResult = await ValidateCanManageMembersAsync(request);
+        if (canManageResult.IsError)
+        {
+            return Invalid(request, canManageResult.AsError);
+        }
+
+        // The acting user can manage members; confirm the target's role is within their authority. A provider
+        // user has Owner-level authority, so treat them as an Owner. The expensive provider lookup already ran
+        // inside the gate above, so we reuse the cheap synchronous role check here rather than repeating it.
+        var effectiveRole = IsAuthorizedByRole(request) ? request.ActingUserRole : OrganizationUserType.Owner;
+
+        return request.TargetUserRole switch
+        {
+            OrganizationUserType.Owner when effectiveRole is OrganizationUserType.Owner => Valid(request),
+            OrganizationUserType.Admin when effectiveRole is OrganizationUserType.Owner or OrganizationUserType.Admin => Valid(request),
+            OrganizationUserType.User or OrganizationUserType.Custom
+                when effectiveRole is OrganizationUserType.Owner or OrganizationUserType.Admin or OrganizationUserType.Custom => Valid(request),
+            _ => Invalid(request, new CannotManageHigherRoleError())
+        };
+    }
+
+    /// <summary>
+    /// Whether the acting user can manage members by their organization role alone, without the provider lookup:
+    /// Owners and Admins always, and Custom users holding the action's permission. Cheap and synchronous, so it
+    /// is safe to evaluate more than once.
+    /// </summary>
+    private static bool IsAuthorizedByRole(OrganizationUserManageMembersRequest request) =>
+        request.ActingUserRole switch
+        {
+            OrganizationUserType.Owner => true,
+            OrganizationUserType.Admin => true,
+            OrganizationUserType.Custom when request.ActingUserPermissions != null
+                && request.PermissionPicker(request.ActingUserPermissions) => true,
+            _ => false
+        };
+}
diff --git a/test/Core.Test/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidatorTests.cs b/test/Core.Test/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidatorTests.cs
new file mode 100644
index 000000000000..505a55e94ed0
--- /dev/null
+++ b/test/Core.Test/AdminConsole/OrganizationFeatures/OrganizationUsers/OrganizationUserAction/OrganizationUserActionValidatorTests.cs
@@ -0,0 +1,207 @@
+using Bit.Core.AdminConsole.OrganizationFeatures.OrganizationUsers.OrganizationUserAction;
+using Bit.Core.Enums;
+using Bit.Core.Models.Data;
+using Xunit;
+
+namespace Bit.Core.Test.AdminConsole.OrganizationFeatures.OrganizationUsers.OrganizationUserAction;
+
+public class OrganizationUserActionValidatorTests
+{
+    private static OrganizationUserActionRequest BuildRequest(
+        OrganizationUserType? actingRole,
+        OrganizationUserType targetRole,
+        bool hasManagePermission = false,
+        bool isProvider = false)
+    {
+        // A null acting role represents a non-member (e.g. a provider-only user).
+        var permissions = actingRole is null
+            ? null
+            : new Permissions { ManageUsers = hasManagePermission };
+
+        return new OrganizationUserActionRequest(
+            actingRole,
+            permissions,
+            p => p.ManageUsers,
+            () => Task.FromResult(isProvider),
+            targetRole);
+    }
+
+    private static OrganizationUserManageMembersRequest BuildManageMembersRequest(
+        OrganizationUserType? actingRole,
+        bool hasManagePermission = false,
+        bool isProvider = false)
+    {
+        // A null acting role represents a non-member (e.g. a provider-only user).
+        var permissions = actingRole is null
+            ? null
+            : new Permissions { ManageUsers = hasManagePermission };
+
+        return new OrganizationUserManageMembersRequest(
+            actingRole,
+            permissions,
+            p => p.ManageUsers,
+            () => Task.FromResult(isProvider));
+    }
+
+    [Theory]
+    [InlineData(OrganizationUserType.Owner, false, OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Owner, false, OrganizationUserType.Admin)]
+    [InlineData(OrganizationUserType.Owner, false, OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.Owner, false, OrganizationUserType.Custom)]
+    [InlineData(OrganizationUserType.Admin, false, OrganizationUserType.Admin)]
+    [InlineData(OrganizationUserType.Admin, false, OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.Admin, false, OrganizationUserType.Custom)]
+    [InlineData(OrganizationUserType.Custom, true, OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.Custom, true, OrganizationUserType.Custom)]
+    public async Task ValidateAsync_WhenActingUserCanManageTargetRole_ReturnsSuccess(
+        OrganizationUserType actingRole,
+        bool actingUserHasManagePermission,
+        OrganizationUserType targetRole)
+    {
+        // Note: Owners and Admins manage by role, so the manage permission is irrelevant for them.
+        var request = BuildRequest(actingRole, targetRole, hasManagePermission: actingUserHasManagePermission);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsValid);
+    }
+
+    [Theory]
+    [InlineData(OrganizationUserType.Admin, true, OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Custom, true, OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Custom, true, OrganizationUserType.Admin)]
+    public async Task ValidateAsync_WhenTargetRoleOutranksActingUser_ReturnsCannotManageHigherRoleError(
+        OrganizationUserType actingRole,
+        bool actingUserHasManagePermission,
+        OrganizationUserType targetRole)
+    {
+        var request = BuildRequest(actingRole, targetRole, hasManagePermission: actingUserHasManagePermission);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsError);
+        Assert.IsType<CannotManageHigherRoleError>(result.AsError);
+    }
+
+    [Theory]
+    // A regular User cannot manage any member, regardless of target role.
+    [InlineData(OrganizationUserType.User, OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.User, OrganizationUserType.Admin)]
+    [InlineData(OrganizationUserType.User, OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.User, OrganizationUserType.Custom)]
+    public async Task ValidateAsync_WhenActingUserIsRegularUser_ReturnsMissingManagePermissionError(
+        OrganizationUserType actingRole,
+        OrganizationUserType targetRole)
+    {
+        var request = BuildRequest(actingRole, targetRole);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsError);
+        Assert.IsType<MissingManagePermissionError>(result.AsError);
+    }
+
+    [Theory]
+    // A Custom user without the manage permission has no authority over any member.
+    [InlineData(OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Admin)]
+    [InlineData(OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.Custom)]
+    public async Task ValidateAsync_WhenCustomUserLacksManagePermission_ReturnsMissingManagePermissionError(
+        OrganizationUserType targetRole)
+    {
+        var request = BuildRequest(OrganizationUserType.Custom, targetRole, hasManagePermission: false);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsError);
+        Assert.IsType<MissingManagePermissionError>(result.AsError);
+    }
+
+    [Theory]
+    [InlineData(OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Admin)]
+    [InlineData(OrganizationUserType.User)]
+    [InlineData(OrganizationUserType.Custom)]
+    public async Task ValidateAsync_WhenActingUserIsProvider_ReturnsSuccessForAnyTargetRole(
+        OrganizationUserType targetRole)
+    {
+        // A provider user has Owner-level authority. They are not a member of the organization, so their
+        // role/permissions are null and authority comes solely from the provider callback.
+        var request = BuildRequest(actingRole: null, targetRole, isProvider: true);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsValid);
+    }
+
+    [Fact]
+    public async Task ValidateAsync_WhenAuthorizedByRole_DoesNotInvokeProviderCallback()
+    {
+        // The provider check hits the database, so it must not be invoked when the role/permission checks
+        // already authorize the action.
+        var providerCallbackInvoked = false;
+        var request = new OrganizationUserActionRequest(
+            OrganizationUserType.Owner,
+            new Permissions(),
+            p => p.ManageUsers,
+            () =>
+            {
+                providerCallbackInvoked = true;
+                return Task.FromResult(false);
+            },
+            OrganizationUserType.User);
+
+        var result = await OrganizationUserActionValidator.ValidateAsync(request);
+
+        Assert.True(result.IsValid);
+        Assert.False(providerCallbackInvoked);
+    }
+
+    [Theory]
+    [InlineData(OrganizationUserType.Owner)]
+    [InlineData(OrganizationUserType.Admin)]
+    public async Task ValidateCanManageMembersAsync_WhenOwnerOrAdmin_ReturnsSuccess(
+        OrganizationUserType actingRole)
+    {
+        var request = BuildManageMembersRequest(actingRole);
+
+        var result = await OrganizationUserActionValidator.ValidateCanManageMembersAsync(request);
+
+        Assert.True(result.IsValid);
+    }
+
+    [Theory]
+    [InlineData(true)]
+    [InlineData(false)]
+    public async Task ValidateCanManageMembersAsync_WhenCustomUser_DependsOnManagePermission(
+        bool hasManagePermission)
+    {
+        var request = BuildManageMembersRequest(OrganizationUserType.Custom, hasManagePermission);
+
+        var result = await OrganizationUserActionValidator.ValidateCanManageMembersAsync(request);
+
+        Assert.Equal(hasManagePermission, result.IsValid);
+    }
+
+    [Fact]
+    public async Task ValidateCanManageMembersAsync_WhenProvider_ReturnsSuccess()
+    {
+        var request = BuildManageMembersRequest(actingRole: null, isProvider: true);
+
+        var result = await OrganizationUserActionValidator.ValidateCanManageMembersAsync(request);
+
+        Assert.True(result.IsValid);
+    }
+
+    [Fact]
+    public async Task ValidateCanManageMembersAsync_WhenRegularUser_ReturnsMissingManagePermissionError()
+    {
+        var request = BuildManageMembersRequest(OrganizationUserType.User);
+
+        var result = await OrganizationUserActionValidator.ValidateCanManageMembersAsync(request);
+
+        Assert.True(result.IsError);
+        Assert.IsType<MissingManagePermissionError>(result.AsError);
+    }
+}