Coach-builder and patron of the arts. Born in Glasgow, McLellan studied at the University of Glasgow before entering his father's coach-building company.
McLellan was a patron of the arts and maintained friendships with many artists, including Sir David Wilkie (1785 - 1841) and Sir Francis Chantrey (1781 - 1841). He was an enthusiastic and discriminating collector, who spent much of his wealth on art and commissioned galleries in Glasgow to hold it. His collection included paintings, sculpture, gold and silver plate. He also encouraged the city to refurbish their Cathedral and contributed architectural advice to this end.
McLellan served as a Magistrate and Town-Councillor in Glasgow.
He died at Mugdock Castle (Stirling) deeply in debt. The Glasgow city fathers took advantage of the opportunity, paying the executors of McLellan's estate £44,500 for his galleries and their contents, thus creating the nucleus of a public collection, which had been McLellan's wish. The McLellan Galleries remain on their original site on Sauchiehall Street.