Franken achieved prominence as a writer and performer for the television show Saturday Night Live from its inception in 1975 before moving to writing and acting in films and television shows. He then became a political commentator, author of five books and host of a nationally syndicated radio show on the Air America Radio network.

In 2008, Franken narrowly defeated incumbent Republican Senator Norm Coleman, by 312 votes, after a mandatory statewide manual recount. Coleman contested the outcome in court, but the Minnesota Supreme Court unanimously upheld Franken's victory on June 30, 2009. Franken was sworn in to the Senate on July 7, 2009.

Franken was born in New York City to Phoebe G. Kunst, a homemaker and real estate agent, and Joseph P. Franken, a printing salesman. The family later moved to St. Louis Park, a suburb near Minneapolis. Franken had a Jewish upbringing. His older brother Owen is a photojournalist; MSNBC's Bob Franken is his cousin. Franken graduated in 1969 from The Blake School, where he was on the wrestling team. He attended Harvard College and graduated cum laude in 1973 with a B.A. in political science.

Franken met his wife, Franni (née Bryson), in his first year of college. In 2005, they moved to Minnesota, and they now reside in Minneapolis.

The Frankens have two children: daughter Thomasin (born 1981) is a Harvard-educated former elementary school teacher turned "food educator and private chef"; son Joe (born 1984) holds a degree in Mechanical Engineering from Princeton.

Franken began his performing career in high school at The Blake School, where he and long-time writing partner Tom Davis were known for their humor. Franken honed his writing and performing skills at Minneapolis' Dudley Riggs' Brave New Workshop theater, specializing in political satire. He and Davis soon found themselves in "a life of near-total failure on the fringes of show business in Los Angeles."

Franken and Davis were recruited as two of the original writers (and occasional performers) on Saturday Night Live (1975–1980, 1985–1995). In the latter case, only Franken returned as a performer, while Davis usually stayed behind the camera.

In Season 1 of "SNL", as apprentice writers, the two shared a salary of $350 per week. Franken received seven Emmy nominations and three Emmy Awards for his television writing and producing. He created such characters as self-help guru Stuart Smalley and such routines as proclaiming the 1980s to be the "Al Franken Decade." Franken was associated with SNL for over 15 years and, in 2002, interviewed former Vice President Al Gore while in character as Smalley. Franken and Davis wrote the script to the 1986 comedy film One More Saturday Night, appearing in it as rock singers in a band called "Bad Mouth." They also appeared in cameo roles in The Rutles: All You Need Is Cash and in the Eddie Murphy and Dan Aykroyd film Trading Places.

Franken's most notorious SNL performance may have been "A Limo for the Lame-O," a commentary he delivered near the end of the 1979–80 season during a "Weekend Update" broadcast. Franken mocked controversial NBC president Fred Silverman as "a total unequivocal failure" and displayed a chart showing the poor ratings of NBC programs. Franken proclaimed that Silverman did not deserve a limousine. As a result of this sketch, Silverman nixed Lorne Michaels' request that Franken succeed him as SNL's head producer, prompting Franken to leave the show when Michaels did, at the end of the 1979–80 season. Franken later returned to the series in 1985, mostly as a writer, but also as an occasional performer best-known for the Stuart Smalley character. He acknowledged using cocaine while working for Saturday Night Live but says he no longer uses any illegal drugs. Franken left the show in 1995 in protest over losing the role of "Weekend Update" anchor to Norm Macdonald.

Franken is the author of five New York Times best-selling books, three of which reached #1, including Rush Limbaugh Is a Big Fat Idiot and Other Observations.