At 70 years old, Mary Steenburgen has this physical status:
Steenburgen moved to Manhattan in 1972 after the Neighborhood Playhouse offered her an opportunity to study acting. She worked as a server at The Magic Pan and for Doubleday while studying under William Esper.
Steenburgen's break came when she was discovered by Jack Nicholson in the reception room of Paramount's New York office and was cast as the female lead in his second directorial work, the 1978 Western Goin' South.
Steenburgen had a leading role, for which she won the Saturn Award for Best Actress, in the 1979 film Time After Time, as a modern woman who falls in love with author H. G. Wells, played by Malcolm McDowell, whom she married the following year.
In her third film, she won the Academy Award for Best Supporting Actress for the 1980 film Melvin and Howard, playing Lynda Dummar, the wife of Melvin Dummar, then a trucker and aspiring singer, who claimed to have befriended reclusive eccentric Howard Hughes. Another notable film appearance came in the well-received 1983 film Cross Creek, portraying Marjorie Kinnan Rawlings, author of The Yearling. In 1985, she also starred in the movie One Magic Christmas as a mother and wife who falls on devastating times at Christmas only to rely on a Christmas miracle to save her family. In 1989, she played Karen Buckman in Parenthood. In Back to the Future Part III (1990), Steenburgen played Clara Clayton, a school teacher who falls in love with Doc Brown. She was persuaded to play the role by her children, as well as by fans of the Back to the Future films, and reprised the role by providing the character's voice in Back to the Future: The Animated Series.
Other performances have been: in What's Eating Gilbert Grape (1993), as a woman who is having an affair with the title character; My Summer Story (1994), as the mother of Ralphie Parker (the sequel to A Christmas Story); the role of Hannah Nixon in the Oliver Stone biopic, Nixon (1995); and the Will Ferrell 2003 comedy Elf, as a woman who discovers that her husband is the father of one of Santa's elves.
She has appeared in the comedy films Step Brothers (2008), playing the mother of Will Ferrell's character; Four Christmases (2008); and The Proposal (2009).
Dirty Girl, which featured Steenburgen, premiered at the Toronto International Film Festival on September 12, 2010. She also appeared in the critically acclaimed film The Help (2011) and had a featured role as a lounge singer, who is the romantic interest in a love triangle, in the 2013 comedy Last Vegas.
She had a small part in the 2015 film A Walk in the Woods as Jeannie. In 2018, Steenburgen starred in the romantic comedy film Book Club.
In television, Steenburgen appeared as Kate Montgomery in Ink (1996) and co-starred as Mary Gulliver in Gulliver's Travels (1996). She has a recurring role as herself in Curb Your Enthusiasm. Steenburgen co-starred as Helen Girardi, the mother of Amber Tamblyn's title character in Joan of Arcadia. In 2011, she had a recurring role as Josephine in the HBO sitcom Bored to Death. Steenburgen starred as Anastasia Lee in the 2011 FX pilot, Outlaw Country, but it was passed by the network. She appeared in the dark sitcom Wilfred from 2011 through 2013 as Catherine Newman, the title character's eccentric and mentally ill mother. Steenburgen had a recurring role on the NBC sitcom 30 Rock from 2012 to 2013 where she played Diana Jessup.
In 2014, she began a recurring role as former Dixie Mafia boss Katherine Hale in the fifth and sixth seasons of Justified.
From 2015 to 2018, she starred as Gail Klosterman on the comedy series The Last Man on Earth.
From 2020 to 2021, she played the role of Maggie Clarke in the NBC musical comedy-drama series Zoey's Extraordinary Playlist for two seasons. She reprised the role for The Roku Channel television film Zoey's Extraordinary Christmas.
In 2007, Steenburgen underwent minor surgery on her arm, which required a general anesthetic; shortly thereafter, she began experiencing "music (...) playing in her head day and night". She subsequently took music lessons so that she could write down what she was hearing, and by 2013 had almost 50 songwriting credits. She has collaborated with musicians from Nashville and was also signed to Universal Music as a songwriter. She performs one of her own songs in Last Vegas.
In 2018, her composition "Glasgow (No Place Like Home)" as performed by Jessie Buckley featured as the climactic musical moment in the film Wild Rose and won Steenburgen several awards, including Critics Choice Award. On October 30, 2020, Steenburgen signed a global publishing deal with Universal Music Publishing Group.