Rashad (Gem of the Ocean, A Raisin in the Sun, "The Cosby Show") succeeds Oscar winner Estelle Parsons, who will help launch the national tour of Tracy Letts' Tony-winning, Pulitzer Prize-honored dark comedy.
Also on May 26, original cast member and Tony nominee Amy Morton rejoins the troupe, as daughter Barbara, replacing Johanna Day.
Rashad appears in a strictly limited engagement through Aug. 23.
(Between May 18-25, understudy and original company member Susanne Marley played Violet.)
Letts' comic drama about a dysfunctional Plains family that reunites when the patriarch goes missing won the Pulitzer Prize for Drama and the 2008 Tony Award for Best New Play.
August: Osage County currently stars Elizabeth Ashley as Mattie Fae Aiken, with Anne Berkowitz, Guy Boyd, John Cullum, Kimberly Guerrero, Brian Kerwin, Mariann Mayberry, Michael Milligan, Sally Murphy, Troy West and Frank Wood.
The three-act, three-and-a-half hour play is currently performed Tuesday at 7 PM, Wednesday-Friday at 7:30 PM, Wednesday and Saturdays at 2 PM, Saturdays at 8 PM and Sundays at 3 PM.
Tickets can be purchased at Telecharge.com, or by calling (212) 239-6200, or (800) 432-7250.
The Music Box Theatre is located at 239 West 45th Street.
The national tour of August: Osage County launches July 24-Aug. 8 in Denver at the Ellie Caukins Opera House before moving to San Francisco's Curran Theatre Aug. 11-Sept. 6.
Parsons joined the Broadway company in June 2008, taking over for Tony winner Deanna Dunagan, who went on to play the role in London.
August: Osage County is produced by Jeffrey Richards, Jean Doumanian, Steve Traxler and Jerry Frankel. Anna D. Shapiro directs and won a Tony for her work.