Kate McGarrigle, who has died aged 63, was a luminous singer and songwriter whose partnership with her sister Anna produced some of the most attractive and memorable music to come out of the North American folk scene in the past 35 years. Their first album, unobtrusively presented with a grainy black-and-white close-up photograph and simply titled Kate & Anna McGarrigle (1976), captivated listeners with its heart-rending harmonies and anthemic songs such as Kate's Talk to Me of Mendocino and Anna's Heart Like a Wheel. In small print on the sleeve was a thank you to friends and family for looking after "Little Rufus", Kate's son with the singer-songwriter Loudon Wainwright III. Both Rufus Wainwright and his younger sister Martha have carried on the family tradition of innovative music-making.
The McGarrigle sisters, Kate, Anna and Jane, grew up in Saint Sauveur des Monts, Québec, where they learned songs from their French-Canadian mother Gaby, and piano from their father Frank and nuns in the village. Later they picked up the guitar, banjo and accordion, and in the early 1960s, with a couple of friends, formed a coffeehouse folk group, the Mountain City Four. After graduating from McGill University, where she studied engineering, Kate sang and played in a duo on the folkclub circuit with Roma Baran, touring the north-eastern US. Their performance at the 1970 Philadelphia Folk Festival elicited a song by Loudon; he and Kate married soon afterwards, went busking in London, then settled in upstate New York, where Rufus was born in 1973.
Kate's first experience of the New York folk scene in Greenwich Village had not impressed her. She contacted Anna, who was working in Montreal, and they began circulating tapes of their songs. Heart Like a Wheel was taken up by Linda Ronstadt, who made it the title of what would be a hugely successful album, while Kate's composition Work Song was recorded by Maria Muldaur on the eponymous LP that succeeded her hit Midnight at the Oasis (1974).
With songwriting credits such as these, the McGarrigles were on the way to their own recording deal, and in 1975 they signed with Warner Brothers and made their first album. The British were quick to appreciate it, and the sisters promptly gathered some friends to play with them and flew to London, where they gave endearingly ramshackle shows. Martha was born soon afterwards, but later that year Kate and Loudon Wainwright's uneasy relationship, which he charted in Red Guitar and other songs, splintered into an acrimonious divorce.
Kate and Anna continued to produce finely crafted albums such as Dancer With Bruised Knees (1977), Pronto Monto (1978), Entre Lajeunesse et la Sagesse (1980) – also known as The French Record – and Love Over and Over (1982). The critic Robert Christgau echoed many of their admirers when he described them as "prim, wry and sexy all at once".
They took a break from recording for much of the 80s, returning in 1990 with Heartbeats Accelerating, of which The New York Times said, of Kate's song I Eat Dinner: "Had Emily Dickinson been a late-20th century songwriter, this might be just the sort of piece she would have written."
Further albums in the 90s, Matapédia and The McGarrigle Hour, both won Juno awards as the best Canadian roots album of the year. A second French-language album, La Vache Qui Pleure, appeared in 2003, and the sisters' last studio work together was The McGarrigle Christmas Hour in 2005.
Between these occasional albums, Kate and Anna collaborated with Emmylou Harris on her album Wrecking Ball, with Joan Baez on Ring Them Bells, and with the Québecois singer Gilles Vigneault. In the late 90s, after the reissue on CD of the 1952 record set Anthology of American Folk Music, six LPs of early blues and country music that had inspired a generation of performers, the McGarrigles participated in concerts in New York, Los Angeles and London, organised by the producer Hal Willner, in memory of the records' compiler, Harry Smith, the ethnologist, film-maker and eccentric. The shows led to collaborations with Geoff Muldaur and Nick Cave.
Kate was extensively honoured, with her sister, in Canadian film and TV documentaries, and in 1994 they were both awarded the Order of Canada.
Kate had suffered from cancer for several years and, in gratitude for the care she had received, had endowed a fund at her old university to support cancer research and care in Montreal. Last week Rufus cancelled a planned Australasian tour to be with her. He and Martha survive her, as do Anna and Jane.
• Kate McGarrigle, singer and songwriter, born February 6, 1946; died January 18 2010
