Sorley MacLean was born in Òsgaig, Raasay on 26 October 1911; Scottish Gaelic was his first language. Before he went to school at the age of six, he spoke very little English. He was the second of five sons born to Malcolm (1880–1951) and Christina MacLean (1886–1974). The family owned a small croft and ran a tailoring business, but they later gave up the croft to move to a better house, which proved detrimental to their finances when the Great Depression took a high toll on the tailoring business. His brothers were John (1910–1970), a schoolteacher and later rector of Oban High School, who was also a piper; Calum (1915–1960), a noted folklorist and ethnographer; and Alasdair (1918–1999) and Norman (c.1917–c.1980), who became general practitioners. Sorley's two younger sisters, Isobel and Mary, were also schoolteachers. His patronymic was Somhairle mac Chaluim 'ic Chaluim 'ic Iain 'ic Tharmaid 'ic Iain 'ic Tharmaid; he could not trace his genealogy with certainty to the eighth generation.