Geoffrey Castles will conduct the CSO Shell Prom in his first ACT concert

Geoffrey Castles will be conducting the Canberra Symphony Orchestra for the first time on November 30 in the the Shell Prom. It will also mark his professional debut in the city.

The 38-year-old conductor has spent most of his career to date playing in or conducting musical theatre - and some of the shows he's been involved with are excerpted in this year's Proms.

He's also working with two singers, Simon Gleeson and Genevieve Kingsford, with whom he has already collaborated.

The 2019 Shell Prom will include some songs from Les Miserables.

Castles was music director of the 25^th anniversary production in 2014 and he admires the way in which Gleeson, who played Jean Valjean, was able to meet the demands of the role.

Castles became involved with the Shell Prom mid-year when the originally scheduled conductor, Vanessa Scammell, had to withdraw.

"I was her associate on Sweeney Todd - she asked me if I would be interested in taking over the concert for her."

He jumped at the opportunity to conduct the CSO: "A musical theatre orchestra is much smaller - the chance to work with a symphony orchestra I'd never pass up."

Working on the concert program, he says he tried to include something for all tastes so every audience member would have a good time whether or not they'd heard the music before.

While the program was still being finalised, he says it will include many classics.

Among them might be The Trolley Song from the film Meet Me in St Louis - "M-G-M at its finest" - and Anthem from Chess ("It's so lush and beautiful").

There will be a couple of numbers from West Side Story including the balcony scene with its duet of Tonight.

The oldest song is likely to be another duet, Cole Porter's You're the Top from Anything Goes ("The lyrics are so witty"). Purely orchestral numbers will include Richard Rodgers' Carousel Waltz ("To have a symphony orchestra play it is such a treat"), Leonard Bernstein's On The Town Overture and Stephen Sondheim's Finishing the Hat from Sunday in the Park With George.

Castles started learning piano at the age of 10, which he says is "kind of late" but made up for lost time musically: he also took up the flute at 12, the cello at 14 and the French horn at 16. Eventually he decided "piano was the way to go" and also began conducting while in high school.

He studied a Bachelor of Music degree at the Sydney Conservatorium and then began working as a casual musician.

His big break came in 2007 when he was hired as a deputy musician - ("you cover someone when they can't be there") - playing the electronic keyboard in the pit for Priscilla, Queen of the Desert.

The electronic keyboard is not the same as a piano - it requires different skills and techniques - but Castles says he learned on the job and enjoyed working with other musicians in the orchestra pit, which he calls "a slightly volatile environment" - covered over, dark, acoustically challenging (especially if wearing headphones) and, in musicals, playing the same material over and over again.

"It's one thing to say you might play Beethoven's Fifth 11 times over the course of a career - for Les Miserables, I performed eight times for eight months.

"It's quite a little beast with its own unique challenges, playing at concert level eight times a week."

Castles has worked on many shows since in various capacities: performer, assistant music director and music director.

His first show as music director was Mary Poppins. which he took over in Auckland in 2012. He spent two and a half years touring with Aladdin ("well over 800 shows").

He's been rehearsing privately with Gleeson and Kingsford so they will be ready to go when the three come to Canberra. This will help make the couple of days' rehearsal with the orchestra much easier.

"It will be hectic but fun."