Davidson will play Kitty's (Calista Flockhart) first significant other since the death of her husband (Rob Lowe). He will begin appearing in late October or early November.
Davidson is perhaps best known for his work on the Lifetime series "Army Wives." His New York stage credits include Back Back Back and Epic Proportions. He played Brick in the Kennedy Center production of Cat on a Hot Tin Roof opposite Mary Stuart Masterson, to whom he is married.
"Brothers and Sisters" premieres Sept. 26 on ABC.