[1] In 2006 she joined the original West End cast of Wicked as part of the ensemble, later moving to be standby for the role of Elphaba.
[3] Janson has appeared in several shows Off-West End, including Company at the Southwark Playhouse (as Amy), Rooms: A Rock Romance at the Finborough Theatre (as Monica), and Blood Wedding at the Courtyard Theatre[4][5][6] In 2013 she returned to the Menier Chocolate Factory in Candide, playing the role of Paquette.
[11] In 2018 she appeared in a revival of Chess as Florence at the London Colosseum, alongside Michael Ball as Anatoly, Alexandra Burke as Svetlana, and Tim Howar as Freddie.
[12] In April 2019 she appeared in Man of La Mancha at the London Colosseum, sharing the roles of Aldonza and Dulcinea with Danielle de Niese.
In 2017 Janson teamed up with Beverley Knight and Amber Riley to form a musical theatre supergroup, known collectively as the "Leading Ladies".