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 (née 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.

During the 63rd Primetime Emmy Awards, Baldwin was slated to appear in a taped skit. However, the producers of the show cut a portion of the skit containing a reference to Rupert Murdoch and the News International phone hacking scandal. Baldwin subsequently boycotted the Emmy Awards and requested that his entire appearance be removed from the broadcast. Producers complied and he was replaced with Leonard Nimoy.

Baldwin attended Alfred G. Berner High School in Massapequa and played football there under Coach Bob Reifsnyder. In New York City, Baldwin worked as a busboy at the disco Studio 54. From 1976 to 1979, he attended George Washington University. In 1979, he lost the election for student body President and received a personal letter from former U.S. President Richard Nixon (with whom he had a Common friend) encouraging him to use the loss as a learning experience.

Baldwin's first acting role was as Billy Aldrich in the NBC daytime soap opera The Doctors from 1980 to 1982. In fall 1983, he starred in the short-lived television series Cutter to Houston. He went on to appear as the brother of Valene Ewing and son of Lilimae Clements (played by Joan Van Ark and Julie Harris, respectively) in Knots Landing from 1984 to 1985. In 1986, Baldwin starred in Dress Gray, a four-hour made-for-television miniseries, as an honest cadet sergeant who tries to solve the mystery of a murdered gay classmate. In 1998, he became the third narrator and George Carlin's replacement for the fifth and sixth seasons of Thomas the Tank Engine & Friends. In 2000, he starred in "Thomas and the Magic Railroad" as Mister Conductor. He left the Thomas the Tank Engine & Friends series in 2002 on winning the role of Lawrence Quinn in The Cat in the Hat and was replaced by Michael Brandon.

Baldwin made his Broadway debut in 1986 in a revival of Joe Orton's Loot alongside Zoë Wanamaker, Željko 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.

Baldwin made his film debut with a minor role in the 1987 film Forever, Lulu. In 1988, he appeared in Beetlejuice and Working Girl. He gained further recognition as a leading man with his role as Jack Ryan in The Hunt for Red October (1990).

In 1990, Baldwin met Actress Kim Basinger when they played lovers in the film The Marrying Man. They married in 1993 and had a daughter, Ireland, in 1995. They separated in 2000, and finalized a divorce in 2002.

Baldwin met his Future wife Kim Basinger when they played lovers in the 1991 film The Marrying Man. Next, Baldwin played a ferocious sales executive in Glengarry Glen Ross (1992), a part added to the film version of David Mamet's Pulitzer Prize-winning stage play (including the monologue "Coffee's for closers").

Also, in 1994, Baldwin made a foray into pulp fiction-based movies with the role of the title character in The Shadow. The film made $48 million. In 1996 and 1997, he continued to work in several thrillers, including The Edge, The Juror, and Heaven's Prisoners.

In October 1995, Baldwin allegedly assaulted a Photographer for videotaping his wife, Kim Basinger, and their 3-day-old daughter. The couple was returning from the hospital and were confronted by the Photographer outside their Los Angeles home. Whoopi Goldberg praised Baldwin for his actions during her opening monologue while hosting the 68th Academy Awards.

During his appearance on the comedy late night show Late Night with Conan O'Brien on December 11, 1998, eight days before President Bill Clinton was to be impeached, Baldwin said, "If we were in another country ... we would stone Henry Hyde to death and we would go to their homes and kill their wives and their children. We would kill their families, for what they're doing to this country." Baldwin later apologized for the remarks, and the network explained that it was meant as a joke and promised not to re-run it.

Baldwin directed and starred in The Devil and Daniel Webster with Anthony Hopkins, Jennifer Love Hewitt and Dan Aykroyd in 2001. The then-unreleased film became an asset in a federal bank fraud trial when investor Jed Barron was convicted of bank fraud while the movie was in production. The film was eventually acquired by The Yari Group without Baldwin's involvement.

In 2002, Baldwin appeared in two episodes of Friends as Phoebe's overly enthusiastic love interest, Parker. He also portrayed a recurring character in a number of season 7 and 8 episodes of Will & Grace, in which he played Malcolm, a "top secret agent" and the lover of Karen Walker (Megan Mullally). He also guest-starred in the first live episode of the series. Baldwin wrote an episode of Law & Order entitled "Tabloid", which aired in 1998. He played Dr. Barrett Moore, a retired plastic surgeon, in the series Nip/Tuck. He starred as Jack Donaghy on NBC's 30 Rock, which first aired October 2006. He met his Future co-stars Tina Fey and Tracy Morgan while appearing on Saturday Night Live, and is one of only two actors to whom Lorne Michaels has extended a standing offer to host the show should their schedules permit (the other being Christopher Walken). Since season 3, Baldwin was credited as one of 30 Rock's producers.

He appeared in Martin Scorsese's The Aviator (2004) and The Departed (2006). In 2006, he starred in the film Mini's First Time. He performed opposite Sarah Michelle Gellar in Suburban Girl (2007). Two years later, he co-starred in the hit romantic comedy It's Complicated with Meryl Streep and Steve Martin.

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 contended that after seven years of these issues, he hit a breaking point, and on April 11, 2007, left an angry voicemail message in response to another unanswered arranged call, in which Baldwin called his 11-year-old daughter a "rude, thoughtless little pig". He contends that the tape was sold to TMZ which released the recording, despite laws against publishing media related to a minor without the permission of both parents. Baldwin admitted that he made a mistake, but asked not to be judged as a parent based on a bad moment. He later admitted to Playboy in June 2009 that he contemplated suicide over the voicemail that leaked to the public. Of the incident, he said, "I spoke to a lot of professionals, who helped me. If I committed suicide, [ex-wife Kim Basinger's side] would have considered that a victory. Destroying me was their avowed goal."

In late 2008, Baldwin toured in support of the book, speaking about his experiences related in it.

In February 2009, Baldwin spoke out to encourage state Leaders to renew New York's tax break for the film and television industry, stating that if the "tax breaks are not reinstated into the budget, film production in this town is going to collapse and television production is going to collapse and it's all going to go to California".

On May 12, 2010, Baldwin gave a commencement address at New York University and was awarded a Doctor of Fine Arts degree, honoris causa.

Baldwin said in a 2006 interview with The New York Times that if he did become involved in electoral politics, he would prefer to run for Governor of New York. When asked if he was qualified for the office, Baldwin responded that he considered himself more qualified than California Governor Arnold Schwarzenegger. In June 2011, The Daily reported that Baldwin was mulling over a 2013 run for Mayor of New York City in the wake of a potential early race shake-up after candidate Congressman Anthony Weiner's sexting scandal. However, on December 21, 2011, Baldwin said he was abandoning plans to run for the office and would instead continue in his role on 30 Rock.

On April 8, 2012, a 40-year-old French-Canadian Actress, Genevieve Sabourin, was arrested outside Baldwin and his wife's Greenwich Village apartment house and charged with aggravated harassment and stalking. She was released without bail and told not to contact Baldwin. Prosecutors said she and Baldwin had met on a film set more than ten years earlier, and that, beginning in 2011, she began sending him multiple unwanted emails and texts.

Despite demonstrating strong political beliefs throughout his career, in October 2013, Baldwin announced that he would not donate money to political candidates while hosting his talk show Up Late with Alec Baldwin on MSNBC, in accordance with the company's policy.

In 2013, Manhattan prosecutors filed nearly two dozen harassment and stalking charges against her, saying she had continued her unwanted advances. On April 8, she rejected a plea bargain, and a trial date was set for May 13. On November 8, at the end of a non-jury trial, Manhattan Criminal Court Judge Robert Mandelbaum found Sabourin, by then 41, guilty on all counts and sentenced her to 180 days in jail for stalking, attempted aggravated harassment, and harassment, plus 30 days for attempted contempt of court. Sabourin was released from New York City's Rikers Island jail on March 28, 2014.

Baldwin co-starred in Mission: Impossible – Rogue Nation, the fifth installment of the Mission: Impossible series, released on July 31, 2015.

In 2016, Baldwin began hosting a reboot of the game show Match Game on ABC. In 2017, he took over as sole host of TCM's The Essentials following the death of his co-host, Robert Osborne.

Baldwin co-hosted the 82nd Academy Awards with Steve Martin in 2010. He has hosted Saturday Night Live 17 times as of February 11, 2017, and holds the record for most times hosting the show. He also impersonated Republican nominee Donald Trump during SNL's coverage of the 2016 Presidential election, to widespread critical acclaim. In 2017, he won a Primetime Emmy for his portrayal of Trump.

On March 3, 2018, following the broadcast of the 90th Academy Awards, ABC broadcast a preview episode of the talk show Sundays with Alec Baldwin, scheduled to formally debut with a nine-episode order later in the year.