Morissette was born June 1, 1974, in Ottawa, Ontario, Canada, to Teacher Georgia Mary Ann (née Feuerstein) and high-school principal and French Teacher Alan Richard Morissette. She has two siblings: older brother Chad is a Business Entrepreneur, and twin brother (12 minutes older) Wade is a musician. Her Father is of French and Irish descent and her mother has Hungarian ancestry. Her parents were teachers in a military school and due to their work often had to move. From 1977 to 1980 Morissette spent three years of her childhood in Lahr, Germany. When she was six years old, she returned to Ottawa and started to play the piano. In 1981, when she was seven years old, she began dance lessons. Morissette had a Catholic upbringing. She attended Holy Family Catholic School for elementary school and Immaculata High School for Grades 7 and 8 before completing the rest of her high school at Glebe Collegiate Institute (Ottawa). She appeared on the children's television show You Can't Do That on Television for five episodes when she was in elementary school.

In 1986, Morissette had her first stint as an actor: five episodes of the children's television show You Can't Do That on Television. She appeared on stage with the Orpheus Musical Theatre Society in 1985 and 1988.

Morissette dated actor and Comedian Dave Coulier for a short time in the early 1990s. In a 2008 interview with the Calgary Herald, Coulier claimed to be the ex-boyfriend who inspired Morissette's song "You Oughta Know". Morissette, however, has maintained her silence on the subject of the song.

In 1991 MCA Records Canada released Morissette's debut album, Alanis, in Canada only. Morissette co-wrote every track on the album with its Producer, Leslie Howe. The dance-pop album went platinum, and its first single, "Too Hot", reached the top twenty on the RPM singles chart. Subsequent singles "Walk Away" and "Feel Your Love" reached the top 40. Morissette's popularity, style of music and appearance, particularly that of her hair, led her to become known as the Debbie Gibson of Canada; comparisons to Tiffany were also Common. During the same period, she was a concert opening act for Rapper Vanilla Ice. Morissette was nominated for three 1992 Juno Awards: Most Promising Female Vocalist of the Year (which she won), Single of the Year and Best Dance Recording (both for "Too Hot").

In 1992, she released her second album, Now Is the Time, a ballad-driven record that featured less glitzy production than Alanis and contained more thoughtful lyrics. Morissette wrote the songs with the album's Producer, Leslie Howe, and Serge Côté. She said of the album, "people could go, 'Boo, hiss, hiss, this girl's like another Tiffany or whatever.' But the way I look at it ... people will like your next album if it's a suck-ass one." As with Alanis (1991), Now Is the Time (1992) was released only in Canada and produced three top 40 singles—"An Emotion Away", the minor adult contemporary hit "No Apologies" and "(Change Is) Never a Waste of Time". It was a commercial failure, however, selling only a little more than half the copies of her first album. With her two-album deal with MCA Records Canada complete, Morissette was left without a major label contract.

In 1993, Morissette's publisher Leeds Levy at MCA Music Publishing introduced her to manager Scott Welch. Welch told HitQuarters he was impressed by her "spectacular voice", her character and her lyrics. At the time she was still living at home with her parents. Together they decided it would be best for her career to move to Toronto and start writing with other people. After graduating from high school, Morissette moved from Ottawa to Toronto. Her publisher funded part of her development and when she met Producer and Songwriter Glen Ballard, he believed in her talent enough to let her use his studio. The two wrote and recorded Morissette's first internationally released album, Jagged Little Pill, and by the spring of 1995, she had signed a deal with Maverick Records. In the same year she learned how to play guitar. According to manager Welch every label they had approached had passed on Morissette apart from Maverick.

To commemorate the tenth anniversary of Jagged Little Pill (1995), Morissette released a studio acoustic version, Jagged Little Pill Acoustic, in June 2005. The album was released exclusively through Starbucks' Hear Music Retail concept through their coffee shops for a six-week run. The limited availability led to a dispute between Maverick Records and HMV North America, who retaliated by removing Morissette's other albums from sale for the duration of Starbucks's exclusive six-week sale. As of November 2010, Jagged Little Pill Acoustic had sold 372,000 copies in the U.S., and a video for "Hand in My Pocket" received rotation on VH1 in America. The accompanying tour ran for two months in mid-2005, with Morissette playing small theatre venues. During the same period, Morissette was inducted into Canada's Walk of Fame.

Following the stressful tour, Morissette started practicing Iyengar Yoga for balancing, and after the last December 1996 show, she headed to India for six weeks, accompanied by her mother, two aunts and two friends.

Morissette was featured as a guest vocalist on Ringo Starr's cover of "Drift Away" on his 1998 album, Vertical Man, and on the songs "Don't Drink the Water" and "Spoon" on the Dave Matthews Band album Before These Crowded Streets. She recorded the song "Uninvited" for the Soundtrack to the 1998 film City of Angels. Although the track was never commercially released as a single, it received widespread radio airplay in the U.S. At the 1999 Grammy Awards, it won in the categories of Best Rock Song and Best Female Rock Vocal Performance, and was nominated for Best Song Written for a Motion Picture, Television or Other Visual Media. Later in 1998, Morissette released her fourth album, Supposed Former Infatuation Junkie, which she wrote and produced with Glen Ballard.

In 1999, Morissette delved into acting again, for the first time since 1993, appearing as God in the Kevin Smith comedy Dogma and contributing the song "Still" to its Soundtrack. Morissette reprised her role as God for a post-credits scene in Smith's next film, Jay and Silent Bob Strike Back, to literally close the book on the View Askewniverse. She also appeared in the hit HBO comedies Sex and the City and Curb Your Enthusiasm, appeared in the play The Vagina Monologues, and had brief cameos playing herself in the Brazilian hit soap operas "Celebridade" and Malhação.

In 2001, Morissette was featured with Stephanie McKay on the Tricky song "Excess", which is on his album Blowback. Morissette released her fifth studio album, Under Rug Swept, in February 2002. For the first time in her career, she took on the role of sole Writer and Producer of an album. Her band, comprising Joel Shearer, Nick Lashley, Chris Chaney, and Gary Novak, played the majority of the instruments; additional contributions came from Eric Avery, Dean DeLeo, Flea, and Meshell Ndegeocello.

Morissette met Canadian actor Ryan Reynolds at Drew Barrymore's birthday party in 2002, and the couple began dating soon after. They announced their engagement in June 2004. In February 2007, representatives for Morissette and Reynolds announced they had mutually decided to end their engagement. Morissette has stated that her album Flavors of Entanglement was created out of her grief after the break-up, saying that "it was cathartic".

In late 2003, Morissette appeared in the Off-Broadway play The Exonerated as Sunny Jacobs, a death row inmate freed after proof surfaced that she was innocent. In April 2006, MTV News reported that Morissette would reprise her role in The Exonerated in London from May 23 until May 28.

She expanded her acting credentials with the July 2004 release of the Cole Porter biographical film De-Lovely, in which she performed the song "Let's Do It (Let's Fall in Love)" and had a brief role as an anonymous stage performer. In February 2005, she made a guest appearance on the Canadian television show Degrassi: The Next Generation with Dogma co-star Jason Mewes and Director Kevin Smith. Also in 2005, Morissette, then Ryan Reynolds's fiancée, made a cameo appearance as "herself" as a former client of Reynolds' character in the film Just Friends. This scene was deleted from the theatrical release, and is only available on the DVD.

Morissette was raised in a devout Roman Catholic family. She became a US citizen in 2005, while maintaining her Canadian citizenship.

In 2006, she guest starred in an episode of Lifetime's Lovespring International as a homeless woman named Lucinda, three episodes of FX's Nip/Tuck, playing a lesbian named Poppy, and the mockumentary/documentary Pittsburgh as herself.

Morissette performed at a gig for The Nightwatchman, a.k.a. Tom Morello of Rage Against the Machine and Audioslave fame, at the Hotel Café in Los Angeles in April 2007. The following June, she performed "The Star-Spangled Banner" and "O Canada", the American and Canadian national anthems, in Game 4 of the Stanley Cup Finals between the Ottawa Senators and the Anaheim Ducks in Ottawa, Ontario. (The NHL requires arenas to perform both the American and Canadian national anthems at games involving teams from both countries.) In early 2008, Morissette participated in a tour with Matchbox Twenty and Mutemath as a special guest.

Morissette's seventh studio album, Flavors of Entanglement, which was produced by Guy Sigsworth, was released in mid-2008. She has stated that in late 2008, she would embark on a North American headlining tour, but in the meantime she would be promoting the album internationally by performing at shows and festivals and making television and radio appearances. The album's first single was "Underneath", a video for which was submitted to the 2007 Elevate Film Festival, the purpose of which festival was to create documentaries, music videos, narratives and shorts regarding subjects to raise the level of human consciousness on the earth. On October 3, 2008, Morissette released the video for her latest single, "Not as We".

Throughout her teen years and her 20s, Morissette suffered from depression and various eating disorders. She went on to recover from them and started to eat a healthier diet. In 2009, she ran a marathon promoting awareness for the National Eating Disorders Association.

On May 22, 2010, Morissette married Rapper Mario "Souleye" Treadway in a private ceremony at their Los Angeles home. They have a son, Ever Imre Morissette-Treadway (born 2010), and a daughter, Onyx Solace Morissette-Treadway (born 2016).

On November 20, 2011, Morissette appeared at the American Music Awards. When asked about the new album during a short interview, she said she had recorded thirty-one songs, and that the album would "likely be out next year, probably [in] summertime". On December 21, 2011, Morissette performed a duet of "Uninvited" with finalist Josh Krajcik during the performance finale of the X-Factor.

She appeared as Amanda, a former bandmate of main character Ava Alexander (played by Maya Rudolph), in one episode of NBC's Up All Night on February 16, 2012. Rudolph officiated as minister for Morissette's wedding with both performing the explicit version of their hit hip-hop song, "Back It Up (Beep Beep)".

In 2014, Morissette played the role of Marisa Damia, the lover of Architect and designer Eileen Gray, in the film The Price of Desire, directed by Mary McGuckian.

In celebration of the twentieth anniversary of the release of Jagged Little Pill, a new four-disc collector's edition was released on October 30, 2015. The four-disc edition includes remastered audio of the original album as well as an entire disc of 10 unreleased demos from the era, handpicked by Morissette from her archives, offering a deeper and more personal look at the classic album. Also included is a previously unreleased concert from 1995 as well as 2005's Jagged Little Pill Acoustic.

In January 2016 she began an advice column in The Guardian newspaper.

Over a period of 7 years, Morissette's Business manager stole over $5 million from the singer. He admitted his guilt in April 2017 and was sentenced to 6 years in jail.

After a six-year hiatus, Morissette is due to release her ninth studio album some time in 2018.