Baldwin was born April 3, 1958, in Amityville, New York, and raised in the Nassau Shores neighborhood of nearby Massapequa, the eldest son of Carol Newcomb (nee Martineau; born 1930) and Alexander Rae Baldwin Jr. (October 26, 1927 - April 15, 1983), a high school history/social studies teacher and football coach. He has three younger brothers, Daniel, William, and Stephen, who also became actors. He also has two sisters, Beth and Jane. Alec and his siblings were raised as Roman Catholics.

Baldwin made his Broadway debut in 1986 in a revival of Joe Orton's Loot alongside Zoe Wanamaker, Zeljko Ivanek, Joseph Maher, and Charles Keating. This production closed after three months. His other Broadway credits include Caryl Churchill's Serious Money with Kate Nelligan and a revival of Tennessee Williams' A Streetcar Named Desire, for which his performance as Stanley Kowalski garnered a Tony Award nomination for Best Actor. Baldwin also received an Emmy nomination for the 1995 television version of the production, in which both he and Jessica Lange reprised their roles, alongside John Goodman and Diane Lane. In 1998, Baldwin played the title role in Macbeth at The Public Theater alongside Angela Bassett and Liev Schreiber in a production directed by George C. Wolfe. In 2004, Baldwin starred in a revival of Broadway's Twentieth Century about a successful and egomaniacal Broadway director (Baldwin), who has transformed a chorus girl (Anne Heche) into a leading lady.  On June 9, 2005, he appeared in a concert version of the Rodgers and Hammerstein musical South Pacific at Carnegie Hall. He starred as Luther Billis, alongside Reba McEntire as Nellie and Brian Stokes Mitchell as Emile. The production was taped and telecast by PBS on April 26, 2006. In 2006, Baldwin made theater news in Roundabout Theatre Company's Off-Broadway revival of Joe Orton's Entertaining Mr. Sloane. In 2010, Baldwin starred opposite Sam Underwood in a critically acclaimed revival of Peter Shaffer's Equus, directed by Tony Walton at Guild Hall in East Hampton, New York.  Baldwin has returned to Broadway as Harold in Orphans. The show, which opened April 18, 2013, was also to have starred Shia LaBeouf as Treat, but LaBoeuf left the production in rehearsals and was replaced by Ben Foster.

When was his most recent theater performance?
Baldwin has returned to Broadway as Harold in Orphans. The show, which opened April 18, 2013, was also to have starred Shia LaBeouf as Treat,