Donald MacKay was born in 1808, the son of teacher Adam MacKay and Elizabeth MacKay of Watten, near Halkirk. Donald came to Berneray in 1850 as the schoolmaster at the SSPCK school, which was held in one half of his home at Rubha Mor.

In 1852 Donald married Marion Paterson, with whom he was to have nine children. He became the island's registrar in 1856, giving up teaching in 1867. The family moved to a new home in Baile 'Tigh mhicAidh', in 1875. Donald continued as registrar until his death in 1892, at which time assistant registrar Malcolm MacAskill took over the role.