Sir Alan Charles Maclaurin Mackerras, AC, CH, CBE was an Australian conductor. He was an authority on the operas of Janáček and Mozart, and the comic operas of Gilbert and Sullivan. He was long associated with the English National Opera (and its predecessor) and Welsh National Opera and was the first Australian chief conductor of the Sydney Symphony Orchestra.

Mackerras initially attended Sydney Grammar School, and also St Aloysius College in Sydney. While at Sydney Grammar, he showed enormous talent by composing operas and conducting student performances in his early teens. At St Aloysius, he took part in the school's Gilbert and Sullivan productions, playing Kate in The Pirates of Penzance, Leila in Iolanthe and Ko-Ko in The Mikado. At age 16, Mackerras studied oboe, piano and composition at the NSW State Conservatorium of Music.

From 1941 to 1942, Mackerras played the oboe for the J. C. Williamson Company during one of their Gilbert and Sullivan seasons, and he was a rehearsal pianist for the Kirsova ballet company. In 1943, Mackerras joined the ABC Sydney Orchestra as second oboist and at age 19, became principal oboist. On 6 February 1947, Mackerras sailed for England on the RMS Rangitiki intending to pursue conducting. He joined Sadler's Wells Theatre as an orchestral oboist and cor anglais player. He later won a British Council Scholarship, enabling him to study conducting with Václav Talich at the Prague Academy of Music.

Returning to England in 1948, Mackerras rejoined Sadler's Wells as an assistant conductor and began his lifelong association with the Sadler's Wells Opera, now English National Opera.

He was a noted authority on Mozart's operas and those of Sir Arthur Sullivan. His ballet with John Cranko, Pineapple Poll, is an arrangement of Sullivan music with a story based on one of W. S. Gilbert's Bab Ballads. Mackerras later arranged music by Giuseppe Verdi for the ballet The Lady and the Fool.

Mackerras directed the Welsh National Opera from 1987 to 1992 where his successes included Tristan und Isolde, The Yeomen of the Guard, and La clemenza di Tito. Between the years of 1992 and 2004 he was the principal guest conductor of Scottish Chamber Orchestra, Royal Philharmonic Orchestra and San Francisco Orchestra, Philharmonia Orchestra and of the Czech Philharmonic Orchestra. With the Royal Opera, he conducted productions of Gounod's Roméo et Juliette and Handel's Semele. Mackerras also had a long association with the Metropolitan Opera, where he conducted The Makropulos Case, Káťa Kabanová, Le Prophète, Lucia di Lammermoor, Billy Budd, Hansel and Gretel and The Magic Flute.

On 18 December 2008, Mackerras served as the conductor for Alfred Brendel's final concert performance with the Vienna Philharmonic Orchestra. Mackerras's last performance at the BBC Proms included Gilbert and Sullivan's Patience. His final public performance saw him conduct Così fan tutte at Glyndebourne in the summer of 2010.

Mackerras died in London on 14 July 2010 at the age of 84.