Joseph MacKay was born on September 18, 1810, in Kildonan, Highland, Scotland.

He was a businessman and philanthropist. He was educated in Scotland. In 1832, he immigrated to Montreal where he established a wholesale dry goods business. His brother Edward became his partner in 1850 and his nephew, Hugh, in 1856, becoming MacKay Brothers. In 1864, Joseph MacKay became involved in the plans to establish the Presbyterian College of Montreal (opened in 1867). He made several donations and was active in soliciting subscriptions for the college. He also served on its board of managers. His business flourished and in 1875, Joseph and Edward retired, leaving the Mackay Brothers business in the hands of Hugh, assisted by his brothers Robert and James. Joseph became interested in the missionary work of the church and in 1879, he was ordained an elder in the St. Gabriel Street Church. He bequeathed $10,000 to the Presbyterian College, and Edward gave an additional sum of $40,000 at the time of Joseph’s death to endow the Joseph Mackay Chair of Systematic Theology. The MacKays were best known for their support of work with handicapped children. A school, the Protestant Institution for Deaf-Mutes and for the Blind, was established in Montreal in 1869. In 1876, Joseph gave property on Décarie Boulevard, and at his own expense erected a four-storey building. He assumed the presidency, and in 1878, the school was renamed in his honour, the MacKay Institution for Protestant Deaf-Mutes.

He died on June 2, 1881, in Montreal, Quebec.