Sir James Loy MacMillan, CBE (born 16 July 1959) is a Scottish classical composer and conductor.
MacMillan was born at Kilwinning, in North Ayrshire, but lived in the East Ayrshire town of Cumnock until 1977.
He studied composition at the University of Edinburgh with Rita McAllister and Kenneth Leighton, and at Durham University with John Casken, where he gained an undergraduate degree and then a PhD degree in 1987. At Durham he was a member of the College of St Hild and St Bede as an undergraduate student and the Graduate Society while studying for his PhD. He was a lecturer in music at the Victoria University of Manchester from 1986 to 1988. After his studies, MacMillan returned to Scotland, composing prolifically, and becoming Associate Composer with the Scottish Chamber Orchestra, often working on education projects. As a young man he was briefly a member of the Young Communist League.