[5] In January 2017, Xavier's lead performance in Sunset Boulevard (at the London Coliseum) won the 2016 BroadwayWorld UK/West End Award for Best Actor in a New Production of a Musical.

Notable productions in which he has appeared include Joe Gillis in Sunset Boulevard on Broadway,[6] Prince Of Broadway with the theatre director and producer Harold Prince,[7] Miss Saigon, Freddie Eynsford-Hill and 20 years later Professor Henry Higgins in My Fair Lady, Raoul in The Phantom of the Opera, Curly in Oklahoma!, and Captain von Trapp in The Sound of Music.

[9][10] Although Xavier started out primarily as a theatre actor, he has also gained many television and film credits including Lieutenant Hamilton Knox[11] in Outlander (Stars), Christopher Miles in The Blacklist[12] (NBC), Dr. Steph Belcombe[13] in Gentleman Jack (BBC) and series regular DCI Elliott Wallace [14] in season 7 and 8 of Grantchester (ITV).

Paul Gambaccini presented the program at London's Mermaid Theatre, featuring the BBC Concert Orchestra and Xavier as Tony.

[25][26] He also played Artie Green in the BBC Radio 2 live recording of Sunset Boulevard, performed at the Cork Opera House with Michael Ball and Petula Clark.

Regular teachers over the years have included Anna Tringham, Ross Sharkey, Lucinda Lawrence, Brandon Lee Sears, Nicola Coates, Peter Polycarpou and Alex Young.

Students are also taught by guest performers and practitioners including Kerry Ellis, Ramin Karimloo, Rebecca Trehearn, Marc Antolin, Robbie Sherman, Katie Brayben, Louise Dearman, Trevor Dion Nicholas and Matt Henry (singer).