Nan was born in Kentangaval on the Isle of Barra on 12 December 1902. Her father, Hector MacKinnon, was a fisherman. Her mother, Mary MacPhee, kept the household running. The Vatersay where she would eventually settle had no causeway then. It was reachable only by small boat, weather permitting. Kentangaval was a small Gaelic-speaking community on Barra's eastern coast, the kind of place where songs and stories were the wallpaper of daily life. Children learned them by listening. They did not learn them as heritage. They learned them as living language.

Nan's childhood unfolded against a backdrop of land politics that had shaped her family directly. The Highland Clearances of the previous century had emptied much of the Gaelic west. In 1906 and 1907, just before her fourth and fifth birthdays, the Vatersay Raiders, cottars from Barra and the surrounding isles, had seized grazing land on Vatersay in defiance of an absentee landlady who had let them go landless. Among the raiders was Neil MacPhee, who wrote songs about Mingulay. Her family had won security of tenure twenty years before she was born, yet the sense of injustice over how unevenly the land had been distributed never quite left. The songs Nan would carry remembered all of it.

James Ross of the School of Scottish Studies described her significance plainly. Nan MacKinnon was not a performer in the modern sense. She was a vessel for an entire culture's memory. She knew lullabies, work songs, laments, love songs, satires, and the kind of biting personal compositions that small communities use to keep each other honest. One catalogued recording is Gura mis tha gu tinn, made in November 1964, a sad and bitter song by a woman who has lost the man she loved to another woman. There are praise songs and milking songs. There are songs that no one else in the world remembered by the time she sang them into a microphone.

By the late twentieth century, the daily Gaelic of the Barra Isles was contracting under the pressure of English-language schooling, broadcasting, and emigration. The old songs were not being sung in kitchens any longer. They were becoming museum pieces. Nan MacKinnon's recordings, more than a thousand tracks now hosted by Tobar an Dualchais, the Kist o Riches, were one of the great acts of cultural preservation in modern Scottish history. She died on 24 June 1982. Vatersay is still inhabited. The causeway to Barra opened nine years after her death, in 1991. The songs she carried are now sung by people she never met, in classrooms and concert halls and recording studios, in a language she would have recognised as the one spoken at her family's hearth on Barra a hundred and twenty years ago.