Walsh was born on March 15, 1950, in Auburn, New York. According to his official website, his show business journey began at age five when he was enrolled at the Irma Baker School of Dance. Billed as Thomas J. Walsh, he made his Broadway debut in 1973 in Seesaw alongside Tommy Tune, who would become a friend and frequent collaborator. By 1975, he was creating the role of Bobby in the original Broadway production of A Chorus Line and later co-wrote a book about the musical, On the Line, chronicling its early beginnings. Walsh was credited as Tune's associate choreographer for the 1978 hit musical The Best Little Whorehouse in Texas and did musical staging for The 1940's Radio Hour the following year. He and Tune received Tony Awards in 1980 for their choreography of A Day in Hollywood/A Night in the Ukraine, and Walsh won a solo Tony for his choreography and was nominated for Best Director in 1983 for the hit musical My One and Only, starring Tune and Twiggy. His third Tony nomination, for the choreography of Nine, came in 1982. Walsh's other Broadway credits as a choreographer included My Favorite Year and Do Black Patent Leather Shoes Really Reflect Up?