Callum Au is a British composer, arranger, orchestrator, and trombonist. He writes music across genres and specializes in writing for big band and large jazz ensemble. He is highly regarded for his stylistic awareness and versatility and has written music to be performed and recorded by some of the world's biggest artists.

Over the past ten years, Callum has established himself as one of the busiest arrangers and orchestrators in the U.K. He has had the privilege of writing music for many international artists, including Jamie Cullum, Randy Brecker, the Royal Philharmonic Orchestra, and Burt Bacharach. In 2016 he was commissioned to arrange I Can't Stop Loving You for Quincy Jones's 80th birthday concert at the BBC Proms with the Metropole Orchestra. That same year, he arranged and orchestrated Jessie J's Christmas single The Man with the Bag. More recent arranging and orchestration work includes the Friday Night is Music Night Live series with Tom Chaplin & Imelda May, the big band scenes in the hit film A Royal Night Out, and Beverley Knight's 25th anniversary concert at the Festival Hall. A fascination with the classic arrangements of Billy May and Nelson Riddle has seen him transcribe several hundred classic big band vocal charts of the '50s and '60s, and through this, he has worked with many of the world's finest jazz singers, including Matthew Ford, Claire Martin, Clare Teal and Dee Dee Bridgewater. In 2015, in a relatively inauspicious green room at the Apex Theatre in Bury St Edmunds, Callum started working on an arrangement of the Disney song Let it Go with high note trumpet superstar Louis Dowdeswell. Thence came an incredibly fruitful collaboration that ultimately resulted in Louis's 2018 album High Score. Since then, Callum's extended big band arrangements have amassed over 8 million views on Louis's YouTube channel, now the most viewed big band channel on YouTube, and due to their successful partnership, Callum and Louis have set up shop at Stadium Studios in Wembley, a project studio where they have since recorded for many of the country's top artists.

As well as being in demand as an arranger and orchestrator, Callum has been a member of the Ronnie Scott's Jazz Orchestra (RSJO) since 2012 as a trombonist. Led by clarinettist and bon vivant Peter Long, the RSJO is one of the U.K.'s premier large jazz ensembles, with a performance schedule to match. In his capacity as a member of the RSJO, Callum has performed alongside top international artists including Curtis Stigers, Seth MacFarlane, Maria Schneider, and at venues including the Cheltenham Festival, the Albert Hall, and Buckingham Palace. He has also composed or arranged a substantial proportion of the band's current working repertoire. Outside of the RSJO, Callum has worked as a freelance trombonist with most of the top big bands and jazz ensembles in the U.K., for multiple West End musicals, at the BBC Proms, and as a session musician on many recordings for film and TV.

Born in London to a Scottish mother and a Chinese father, Callum spent most of his formative years in Blackpool. He was taught throughout his school years by veteran U.K. trumpeter Terry Reaney and, having cut his teeth in the local jazz and dance bands, he joined Bill Ashton's National Youth Jazz Orchestra at the age of 15. During some seven years with NYJO, he played every trombone chair and contributed over a hundred new arrangements to the band's library. A four-year stint at Balliol College followed, where he studied Classics, and, more importantly, ran the Oxford University Big Band. In his spare time, he enjoys fantasy novels, tropical fishkeeping, and strategy games.