The daughter of a nurse mother and a livestock-trading father, McKennitt studied classical piano and voice and learned to dance in the highland style as a youngster. Her love of traditional music was strengthened in the folk clubs of Winnipeg, which she frequented during the brief period she studied veterinary science at the University of Manitoba. Relocating to Stratford, Ontario, she continued to sharpen her skills as a composer and performer. In 1981, she auditioned for a role in the city's Stratford Festival of Canada. Although she did not get the role, she remained inspired. After reading Diane Sward Rapaport's book How to Make and Sell Your Own Recording, she formed her own label, Quinlan Road.

After releasing two albums, a nine-song cassette, Elemental, in 1985, and a collection of Christmas tunes, To Drive the Cold Winter Away, in 1987, she had her first breakthrough with her 1989 album, Parallel Dreams. With the help of a network of small independent distributors, the album sold more than 40,000 copies within four months. Its success was surpassed by McKennitt's fourth album, The Visit. Distributed by Warner Canada, the album sold over 600,000 copies (six times platinum) in Canada and received a Juno Award, as did McKennitt's next recording, The Mask and Mirror, in 1994.

While her albums have featured soothing, ultra-melodic arrangements, McKennitt's lyrics have reflected her interests in the poetry of W.B. Yeats, William Blake, and Alfred Lord Tennyson. Her music has been heard on the soundtracks of numerous plays and films. In 1989, she was commissioned by the National Film Board of Canada to compose the music for a film series, Woman and Spirituality. Her subsequent commissions include such films as Jade, Highlander III, and Disney's The Santa Clause, as well as TV shows including Northern Exposure, Due South, and EZ Streets.

In 1998, McKennitt scored her biggest hit with "The Mummers' Dance." She became a hit in America, which led to The Book of Secrets selling more than four million copies. Sadly, her world crumbled that July when her fiancé, Ronald Rees, died while on a sailing trip with his brother and a family friend in Georgian Bay. Everything stopped immediately in order for McKennitt to grieve. Rumors of her retirement also circulated. At the time of her fiancé's death, McKennitt was mixing a new album, Live in Paris and Toronto, at Peter Gabriel's Real World studios. Recorded in Salle Pleyel in Paris and Massey Hall in Toronto during spring 1998, the album was released in 1999. All profits from the album have gone to the Cook-Rees Memorial Fund, which McKennitt set up to finance water safety initiatives and education across Canada.

In the new millennium, McKennitt allowed herself some healing time. She didn't disappear from music altogether, however, and worked with a number of local and national charities. Her Spanish version of "Dante's Prayer" was featured in the Canadian/Venezuelan feature film A House with a View of the Sea in 2001. In 2002, she headlined a concert in Winnipeg for Queen Elizabeth, and in 2003 she received the Order of Canada. Two years later, McKennitt began work on her seventh studio album, Ancient Muse, which was released in 2006. Nights from the Alhambra, a live CD/DVD, arrived in 2007, followed by Midwinter Night's Dream, a collection of holiday music that included 1995's Winter Garden EP in its entirety, along with eight new recordings. A Mediterranean Odyssey was released in 2009; the two-disc set included Olive and the Cedar, an 11-song compilation of some of her best-loved Mediterranean pieces, along with From Istanbul to Athens, which was recorded live on her 2009 Mediterranean tour.

In 2010, McKennit returned with The Wind That Shakes the Barley, an album that found her revisiting the traditional Celtic style of her earlier work. In 2012, McKennit followed up that studio effort with the live and unplugged concert album Troubadours on the Rhine: A Trio Performance. Nights from the Alhambra, released early in 2014, was drawn from her 2006 tour in support of the Ancient Muse album. The two-disc The Journey So Far: The Best of Loreena McKennitt, which surveyed her three-decade recording career, drew a dozen key songs from her eight studio albums and her single releases and collected them on the first disc, and added a second bonus disc that featured live performances recorded in Mainz, Germany during McKennitt's 2012 A Midsummer's Night tour. ~ Craig Harris