MacDonald was educated at St Paul's School, London and Jesus College, Cambridge, where he initially studied geology and physics, but changed to an arts degree.
In 1966 he joined the BBC, becoming a producer in the drama department, working particularly on anthology play series such as The Wednesday Play (for which he produced some of Dennis Potter's early work), Thirty-Minute Theatre, and Theatre 625.
By this time one of the senior producers working in the BBC's drama department, in 1977 he was promoted to become the Head of Serials.
In 1981, he was promoted again to succeed Shaun Sutton as the overall Head of Drama at BBC Television.
He was controller of the channel until 1987 (combining it with his Head of Drama role until he left this post in 1985), during which the Zircon affair erupted surrounding an edition of the Secret Society documentary series due to be shown on the channel.