Remove unused namespaces across a whole project or solution at once

There is no need for any plugins in VS 2017 or 2019. Click the bulb icon near any using statement and click Solution next to Fix all occurrences in part.

Do you mean using statements? First, note that they generally do no harm other that take space. Tools like ReSharper offer automated tricks to do this, however: there was a link in the VS feed a little while ago; it boils down to:

• go to Tools -> Macros -> Macros IDE...
• in the Project Explorer, Add -> Add Module... (put in a name - I've used OrganiseUsings)
• paste over with the code below
• File -> Save MyMacros, exit

Now if you right-click on the toolbar and Customize... - you should be able to find MyMacros.OrganiseUsings.RemoveAndSortAll - drag this somewhere handy (maybe the Tools menu; you might also want to change the name after placing it).

You can now use this option to run the Remove and Sort command for an entire solution. A big time-saver.

==== code ====

Imports System
Imports EnvDTE
Imports EnvDTE80
Imports EnvDTE90
Imports System.Diagnostics

Public Module OrganiseUsings

    Public Sub RemoveAndSortAll()
        On Error Resume Next
        Dim sol As Solution = DTE.Solution

        For i As Integer = 1 To sol.Projects.Count    
            Dim proj As Project = sol.Projects.Item(i)    
            For j As Integer = 1 To proj.ProjectItems.Count    
                RemoveAndSortSome(proj.ProjectItems.Item(j))    
            Next    
        Next    
    End Sub    

    Private Sub RemoveAndSortSome(ByVal projectItem As ProjectItem)
        On Error Resume Next
        If projectItem.Kind = Constants.vsProjectItemKindPhysicalFile Then    
            If projectItem.Name.LastIndexOf(".cs") = projectItem.Name.Length - 3 Then
                Dim window As Window = projectItem.Open(Constants.vsViewKindCode)

                window.Activate()

                projectItem.Document.DTE.ExecuteCommand("Edit.RemoveAndSort")

                window.Close(vsSaveChanges.vsSaveChangesYes)
            End If    
        End If    

        For i As Integer = 1 To projectItem.ProjectItems.Count    
            RemoveAndSortSome(projectItem.ProjectItems.Item(i))    
        Next
    End Sub   

End Module

There is a built-in function under the analyze menu that is called as Code Cleanup. If you click Profile 1, it'll do as remove and sortings functionality.

If you do mean 'using' Power Commands contains this functionality + a boat load more.

http://code.msdn.microsoft.com/PowerCommands

visual studio 2017 having inbuild feature to remove unnecessary name space from whole project.