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. His father is James MacMillan, a carpenter, and his mother is Ellen MacMillan (née Loy).

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.

He came to the attention of the classical establishment with the BBC Scottish Symphony Orchestra's premiere of The Confession of Isobel Gowdie at the BBC Proms in 1990. Isobel Gowdie was one of many women executed for witchcraft in 17th-century Scotland. According to the composer, "On behalf of the Scottish people the work craves absolution and offers Isobel Gowdie the mercy and humanity that was denied her in the last days of her life."

The work's international acclaim spurred more high-profile commissions, including a percussion concerto for fellow Scot Evelyn Glennie: Veni, Veni, Emmanuel. It was premiered in 1992 and has become MacMillan's most performed work. He was also asked by Mstislav Rostropovich to compose his Cello Concerto, which was premiered by Rostropovich in 1997.

Further successes have included his second opera The Sacrifice, commissioned by Welsh National Opera, Autumn 2007, which won a Royal Philharmonic Society Award, and the St John Passion jointly commissioned by the London Symphony Orchestra and Boston Symphony Orchestra and conducted by Sir Colin Davis at its world premiere in April 2008. He was awarded the British Composer Award for Liturgical Music, for his Strathclyde Motets, in December 2008.

In 2019, The Guardian ranked MacMillan's Stabat Mater the 23rd greatest work of art music since 2000.

In 2024, he was became a Fellow of The Ivors Academy, the 26th person to be so honoured.