At the age of 16, Machin trained at Sylvia Young Theatre School, taking part in an adult drama course.
[1] Through the 1990s and early 2000s she appeared in the ensemble of several major West End shows including roles in Les Misérables, Oliver!
[2] In 2009, Machin played Mamie Eisenhower in the UK professional premiere of First Lady Suite by Michael John LaChiusa, with the Whatsonstage.com review describing her performance as "particularly memorable".
[4] In 2014, she originated the role of Gladys in the West End production of Memphis, for which she was nominated for the Whatsonstage.com Awards for Best Supporting Actress in a Musical.
For this role she was nominated for a Laurence Olivier Award for Best Actress in a Musical alongside fellow cast members Joanna Riding, Claire Moore, Sophie-Louise Dann, Debbie Chazen and Michelle Dotrice.