The TV show, which recently won its fifth Emmy Award for Outstanding Comedy Series, will feature Daly as Mrs. Plank, Lily's old-school teacher.
The episode will also feature guest stars Steve Zahn and Andrea Anders as Ronnie and Kim, who move in next door to the Dunphy family.
Daly won a Tony Award for her performance in Gypsy. She received Tony nominations for Rabbit Hole and Mothers and Sons and has also performed in The Seagull and Master Class. She is an Emmy winner for "Judging Amy," "Christy" and "Cagney & Lacey."
The cast of "Modern Family" includes Ed O'Neill, Sofia Vergara, Julie Bowen, Ty Burrell, Jesse Tyler Ferguson, Eric Stonestreet, Rico Rodriguez, Nolan Gould, Sarah Hyland and Ariel Winter. The series will return Sept. 24 at 9 PM on ABC.