Joni Mitchell was born Roberta Joan Anderson to Bill Anderson and Myrtle Anderson. Her mother was a teacher, and her father an officer in the Royal Canadian Air Force. When she was eleven years old, the family settled in Saskatoon, Saskatchewan, which Mitchell considers her hometown.

At the age of nine, Mitchell contracted polio during a Canadian epidemic, but recovered after a stay in the hospital. It was during this time that she first became interested in singing. She describes her first experience singing while in hospital during the winter in the following way: "They said I might no[t] walk again, and that I would not be able to go home for Christmas. I wouldn't go for it. So I started to sing Christmas carols and I used to sing them real loud....The boy in the bed next to me, you know, used to complain. And I discovered I was a ham."

She began smoking at the age of nine as well, a habit which is debatably one of the factors contributing to the change in her voice in recent years. As a teenager, she taught herself ukulele and, later, guitar and began performing at parties, which eventually led to busking and gigs playing in coffeehouses and other venues in Saskatoon. After finishing high school, she attended the Alberta College of Art and Design in Calgary for a year.

And so, after leaving the art college in June 1964, Mitchell left her home in Saskatoon to relocate to Toronto. Joni also found out that she was pregnant by her college ex-boyfriend, and in February 1965 she gave birth to a baby girl. A few weeks after the birth, Joni married folk-singer Chuck Mitchell, and took his surname. He promised to help take responsibility for the child but something changed, and a few weeks later Joni gave her daughter, Kelly Dale Anderson, up for adoption. The experience remained private for most of her career, but she made allusions to it in several songs, most notably the song "Little Green" (from Blue), and, years later, the song "Chinese Cafe" from Wild Things Run Fast ("Your kids are coming up straight/My child's a stranger/I bore her/But I could not raise her"). Her daughter, renamed Kilauren Gibb, began a search for her as an adult, and the two were reunited in 1997.

In the summer of 1965, Chuck Mitchell took Joni with him to the United States. However, the marriage and partnership of Joan & Chuck Mitchell dissolved in a year and a half, in early 1967. Thereafter, Mitchell launched her solo career.

In early 1967 Joni Mitchell moved to New York City to pursue her musical dreams as a solo artist. She played venues up and down the East Coast, including Philadelphia, Boston, and Fort Bragg, North Carolina. She performed frequently in coffeehouses and folk clubs and, by this time creating her own material, became well known for her unique songwriting and her innovative guitar style.

While she was playing one night in "The Gaslight South", a club in Florida, David Crosby walked in and was immediately struck by her ability and her appeal as an artist. He took her back to Los Angeles, where he set about introducing her and her music to his friends. David convinced a record company to agree to let Joni record a solo acoustic album without all the folk-rock overdubs that were in vogue at the time, and his clout earned him a producer's credit in March 1968, when Reprise records released her debut album, Song to a Seagull.

She continued her steady touring to promote the LP. The touring helped create an eager anticipation for Mitchell's second LP, Clouds, which was released in April 1969. It contained Mitchell's own versions of songs already recorded and being performed by other artists: "Chelsea Morning", "Both Sides Now", and "Tin Angel".

Joni won the Grammy Award in March 1970 for Best Folk Performance of 1969 for her album, Clouds. Reprise released her third album, Ladies of the Canyon, soon after. It was an instant smash on FM radio and sold briskly through the summer and fall, eventually becoming Joni's first gold album.

Joni made a decision to stop touring for a year and just write and paint, yet was still voted Top Female Performer for 1970 by Melody Maker, the UK's leading pop music magazine. The songs she wrote during the months she took off for travel and life experience would appear on her next album, Blue, released in June 1971. Blue was an almost instant critical and commercial success, and peaked in the top 20 in the Billboard Album Charts in September. The album was regarded as a culmination of her inspired early work, with depressed assessments of the world around her serving as counterpoint to exuberant expressions of romantic love.

She made the decision to return to the stage after the great success of Blue and she presented many new songs on that tour that would appear on her later album. Joni's fifth album, For the Roses, was released in October 1972 and immediately zoomed up the charts. She followed with the single, "You Turn Me On, I'm a Radio", which peaked at #25 in the Billboard Charts for two weeks beginning in February 1973, becoming her first bona-fide hit single. The album was critically acclaimed and earned her success on her own terms.

Mitchell's next album, Court and Spark, released in January 1974, was her most commercially successful, critically acclaimed, and widely popular collection of songs; it went all the way to #2 on the Billboard album charts and stayed there for four weeks. It contained such popular tracks as "Free Man in Paris", which was released right before Christmas 1973, and "Help Me", which was released in March of the following year, and became Joni's only Top 10 single when it peaked at #7 in the first week of June.

In January 1975, the Grammy nominations were announced and Mitchell received four nominations, which included being the only female in the Album of the Year contest. However, she won only one for Best Arrangement Accompanying Vocals.

Mitchell went into the studio in the spring of 1975 to record acoustic demos of some songs she'd written since the tour ended. A few months later she recorded band versions of the tunes. This song cycle was released in November 1975 as the album The Hissing of Summer Lawns. The LP was a big seller and peaked at #4 on the Billboard album charts, but generally was not well received at the time of its release. During 1975, Mitchell also participated in several concerts in the Rolling Thunder Revue tours featuring Bob Dylan and Joan Baez

In January 1976, Mitchell received one Grammy nomination as Best Pop Vocal Performance, Female for the album The Hissing of Summer Lawns, though the Grammy went to Linda Ronstadt.

In the summer of 1977, Mitchell began work on what would be her first double studio album. The double LP and cassette, Don Juan's Reckless Daughter, was released in December 1977. The album received mixed reviews but still sold relatively well, peaking at #25 in the US and going gold within three months.

Mitchell continued experimenting with synthesizers, drum machines and sequencers for the recordings of her next album, as well as collaborating with artists including Willie Nelson Billy Idol Wendy and Lisa, Tom Petty Don Henley and Peter Gabriel The album that eventuated was 1988's Chalk Mark in a Rain Storm. The official first single of the album was "My Secret Place", a duet with Peter Gabriel

The album Night Ride Home was released in March 1991. Critically, it was better received than her 80s work and seemed to signal a move closer to her acoustic beginnings. But to many, the real return to form came with 1994's Grammy-winning Turbulent Indigo.

Indigo (1994) was Mitchell's most simple, straightforward set of songs in years, mixing politics ("Sex Kills") with social commentary ("Sunny Sunday", "Borderline") to create "a startling comeback" that won two Grammy awards, including Best Pop Album. The recording of Indigo saw the divorce of Mitchell and bassist Larry Klein, whose marriage had lasted almost 12 years.

Almost every song she composed on the guitar uses an open, or non-standard, tuning; she has written songs in some 50 different tunings, which she has referred to as "Joni's weird chords". In 2003 Rolling Stone named her the 72nd greatest guitarist of all time; she was the highest-ranked woman on the list.