Is this what you are trying? I have commented the code so that you will not have any problem understanding it.
Sub Sample()
Dim ws As Worksheet
Dim lRow As Long, lCol As Long
Dim rng As Range
'~~> Set this to the relevant worksheet
Set ws = [Sheet1]
With ws
'~~> Get the last row and last column
lRow = .Range("A" & .Rows.Count).End(xlUp).Row
lCol = .Cells(1, .Columns.Count).End(xlToLeft).Column
'~~> Set the range
Set rng = .Range(.Cells(lRow, 1), .Cells(lRow, lCol))
With rng
Debug.Print .Address
'
'~~> What ever you want to do with the address
'
End With
End With
End Sub
BTW I am assuming that LastRow is the same for all rows and same goes for the columns. If that is not the case then you will have use .Find to find the Last Row and the Last Column. You might want to see THIS