He later collaborated with Steve Hackett and played in the King Crimson spin-off group 21st Century Schizoid Band.

[2] After leaving the army, McDonald moved back to London, and began making music with his girlfriend, former Fairport Convention singer Judy Dyble.

The pair were introduced to Robert Fripp and Michael Giles which led to the formation of King Crimson.

[7] However, the relationship ended and she left the band before they played their first gig in 1969, by which time McDonald, Fripp and Giles were joined by Greg Lake and Peter Sinfield.

[2] McDonald's saxophone solo was a high point on their track "21st Century Schizoid Man", and he went on to play this on their first album In the Court of the Crimson King.

[2] They formed a duo that released one album titled McDonald and Giles, which featured an orchestral backing instead of a Mellotron as used with King Crimson.

The band included former King Crimson members Michael Giles (drums and percussion), Peter Giles (bass), McDonald (sax, flute, keyboards), Mel Collins (alto/tenor sax, flute, keyboards) and also Jakko Jakszyk, who later joined King Crimson in 2013, on guitar and lead vocals.

[15] Although Foreigner was a more conventional rock band compared to King Crimson, McDonald still made significant contributions to the group's arrangement and production.

McDonald was also a session musician and played on T. Rex's hit "Bang a Gong (Get It On)", where he borrowed Mel Collins' baritone saxophone.

[20] In 2017, McDonald and singer-guitarist Ted Zurkowski formed the band Honey West, which released an album Bad Old World in 2017.

[1][21] A trailer for a King Crimson documentary was released a week before his death, in which McDonald apologised to Fripp for leaving the band in 1970.