Originally, he did not want to see the musical, but a hockey game instead. He fell in love with Phantom and knew he would be performing until he got the title role.
He moved to Richmond Hill from Peterborough and attended Alexander Mackenzie High School.
After dropping out of school at 18, he began his performing career in rock bands, cruises, and various theatre projects before moving on to perform in theatre companies for Airtours and P&O Cruises.
He has played the leading male role in both of the West End's longest running musicals: the Phantom and Raoul, Vicomte de Chagny in The Phantom of the Opera, and Jean Valjean, Enjolras, and Marius Pontmercy in Les Misérables.
Les Misérables was his West End debut; he played Feuilly and understudied the roles of Marius Pontmercy and Enjolras.
After this, in 2003, Karimloo took one of the lead roles, Raoul Vicomte de Chagny, in The Phantom of the Opera.
He also originated the role of the Phantom in Andrew Lloyd Webber's Love Never Dies, which continues the story of The Phantom of the Opera.
He made his Broadway debut as Jean Valjean in the 2014 revival production of Les Misérables, for which he received a Tony Award for Best Actor in a Musical nomination.