Weston will play Barb Tucker, the mother of Cameron (2010 Emmy winner Eric Stonestreet).
Weston received Tony and Drama Desk nominations and an Outer Critics Circle Award for her performance in Alfred Uhry's The Last Night of Ballyhoo. She has also appeared on Broadway in Summer and Smoke, Suddenly Last Summer, Loose Ends and The Lady from Dubuque.
As previously reported, Tony Award winner Nathan Lane will also guest star on the sitcom as Pepper, the much-discussed friend of Cameron and Mitchell (stage vet Jesse Tyler Ferguson).
The second season of "Modern Family" begins Sept. 22 on ABC.
