Maggie Roswell was born and raised in Los Angeles, California. After going to Catholic school and Los Angeles City College, she began a career in acting. In the 1970s, she made some guest appearances on television shows such as M*A*S*H, but she did not gain her first big acting roles until the 1980s. In the 1980 film Midnight Madness, she played a character that leads a group of sorority sisters who are participating in a college puzzle solving race. Roswell also starred in the sketch comedy The Tim Conway Show in 1980 and 1981. She appeared in the film Lost in America (1985) as the character Patty, and she had a supporting role in the film Pretty in Pink (1986). She also acted in the two-part television film The Deliberate Stranger. In addition, Roswell played some minor roles in television shows in the 1980s and the beginning of the 1990s, including guest appearances on Remington Steele (1983), Masquerade (1984), Happy Days (1984), Murphy Brown (1993), and Quantum Leap (1993). She was offered a chance to replace Gilda Radner on Saturday Night Live, but turned down the offer when her agent told her “the show wasn’t going anywhere.”

Roswell has also worked on stage. In 1986 she appeared in improvisatory shows directed by Paul Sills at Lamb’s Theatre, in which the actors were given characters and situations by the audience members. In 1988, she had a role in Julia Sweeney’s play Mea’s Big Apology at Groundling Theatre in Los Angeles. She played Eunice, a cynical woman who works at a malpractice insurance company and is a colleague to the main character. The company people do everything they can to dismiss her because they do not want to pay her retirement benefits, which are about to take effect. Roswell reprised this role in a 1992 revival of the play, also at Groundling Theatre.

Roswell met fellow voice actor Hal Rayle in 1986, and they married in 1987. He had done roles such as the Predator in Predator 2, the ghoulies in Ghoulies II, and Marvin the Martian in Air Jordan commercials. They moved from Los Angeles to Denver, Colorado, in June 1994 to raise their adopted daughter Spenser, who was born in 1993. Between March and November every year, when episodes of The Simpsons were being recorded, Roswell had to fly back to Los Angeles twice a week to attend the table reads and the recording sessions. In an article about her and her husband’s move, Ricky Lopes of Rocky Mountain News wrote: “When The Simpsons is taping, she goes to Los Angeles every Friday morning for the first reading, flies back that afternoon, flies back Sunday to tape the show Monday and flies back home that night.” Maggie Roswell said she “got the idea for the way Helen Lovejoy says ‘B-bye, b-bye, b-bye,’ to everyone when they leave the church from the way the flight attendants say it when you get off the plane.”

In addition to her live action roles, Roswell did some voice acting in animated films and shows, including the voice of Teegra in Fire and Ice from 1983. This led to her being hired on the animated television series The Simpsons in 1989. Her first appearance was in the season one episode “Homer’s Night Out”, in which she voiced the character Princess Kashmir (a belly dancer who seduces Homer). Out of the total thirteen episodes of the first season, Maggie Roswell appeared in four; however, they were only minor roles. Maggie Roswell did not become a regular cast member until the middle of the second season in the episode “Dead Putting Society” (1990), with the introduction of Maude Flanders (neighbor to the Simpson family and the loving wife of Ned Flanders). Maggie Roswell went on to voice other recurring characters on the show, such as Helen Lovejoy (the reverend’s wife), Miss Hoover (an elementary school teacher), and Luann Van Houten (the mother of Bart’s best friend, Milhouse), as well as several more one-time characters and background characters. Fellow Simpsons cast member Nancy Cartwright wrote in her autobiography that “Maggie Roswell has been blessed with a skill in creating one of the hardest things to create: the ‘normal sound,’ whatever that is. So she can easily slip into the gal next door or any number of assorted reporters, medical students, jury members, accountants, scientists and moms.” Roswell was nominated for an Emmy Award for her work on The Simpsons. She also received a 1997 Annie Award nomination in the category “Best Individual Achievement: Voice Acting by a Female Performer in a TV Production” for her role as Shary Bobbins in the episode “Simpsoncalifragilisticexpiala(Annoyed Grunt)cious”, but lost to June Foray.

Roswell and Rayle began writing, producing, and/or voicing advertisements together for companies. They established “The Roswell ‘n’ Rayle Company” for this purpose, and built a recording studio in their basement. In 1994, they did radio advertisements in Denver for Burger King, Christy Sports, and an insect exhibit at the Museum of Natural History. The same year, Roswell provided her voice for Campbell’s Soup and Pontiac commercials as part of their business. The company is still active as of 2010. They are now also providing comedic ring tones.

In 1997, Roswell appeared in the film Switchback alongside Danny Glover and Dennis Quaid.

Roswell left The Simpsons in spring 1999 after a pay dispute with Fox Broadcasting Company, which airs The Simpsons. The dispute was not revealed to the press at first; Fox originally reported that she decided to quit only because she was tired of flying between Denver and Los Angeles for the recording sessions. Then Roswell announced that she had asked for a raise, not only because she was tired of the traveling, but because of the increasing cost of flight tickets. Roswell was paid $1,500 to $2,000 per episode during the three seasons before she left, and she asked Fox for a raise to $6,000 per episode. However, Fox only offered her a $150 raise, which did not even cover the travel costs, so she decided to quit. She told The Denver Post that “they offered me a $150 raise. I mean, that’s lint in Fox’s pocket. But Fox wanted to prove a point, I guess. I was flying myself back and forth from Denver to L.A. It was exhausting. I loved doing the show and they thought that I would come back. But now I’m busy doing other things.” She further added that “I was part of the backbone of The Simpsons and I don’t think the money I asked for was exorbitant. I wasn’t asking for what other cast members make. I was just trying to recoup all the costs I had in travel. If they’d flown me in, I’d still be working.” At that point, the six main cast members of the show were paid $125,000 per episode. As a result of Maggie Roswell’s departure, the Maude Flanders character was killed off in the episode “Alone Again, Natura-Diddily”. Voice actress Marcia Mitzman Gaven was hired to fill in for Maggie Roswell’s other characters.

Roswell enjoys singing. On February 7, 1999, she debuted as a nightclub singer at the Denver Chop House & Brewery, where she performed on behalf of the homelessness charity Family Homestead. In June 2003, she sang at Denver’s Rattlebrain Theatre on Sunday nights with The Sirens.

Roswell returned to The Simpsons in 2002 in the season premiere of the fourteenth season, in which Maude made an appearance as a ghost. She reached a deal with Fox to record her lines from her Denver home, the dispute ended, and Roswell has remained on the show. She also appeared as Helen Lovejoy in the film The Simpsons Movie (2007). She attended the gala premiere together with her daughter, Spenser Rayle, who was fourteen years old at the time. Roswell told The Denver Post that she was surprised she was given two tickets; “Everybody in Hollywood is killing to get their kid there. My daughter’s big thrill is to meet [the band] Green Day,” which also appeared in the film.

In 2004, Roswell had a minor role in the film Silver City. In 2009, she starred in the play Bunny Bunny: Gilda Radner, a Sort of Romantic Comedy at Avenue Theater in Denver. It opened in May of that year. The play recounted events in the career of actress Gilda Radner, who Roswell played, from 1975 (the start of Saturday Night Live) to her death in 1989.