Mahy toured nationally in Grease, playing the role of Kenickie alongside notable cast members Rob Mills, Gretel Scarlett, Anthony Callea, Lucy Maunder, Todd McKenney and Bert Newton as Vince Fontaine.

[2] In 2015, Stephen joined the cast of The Rocky Horror Show, playing the role of Brad Majors alongside Craig McLachlan, Amy Lehpamer, Jayde Westaby, Bert Newton and Richard O'Brien, just to name a few.

He featured in "Stephen Schwartz in Conversation" at Sydney's Theatre Royal, where he performed on stage for the noted composer.

[6] While at the Western Australian Academy of Performing Arts, Mahy appeared in numerous productions, including Bobbin Up, Crazy For You and Elegies.

Mahy performed at the Seniors' Week On Broadway concert in 2012 with Ian Stenlake (Oklahoma, Guys and Dolls), Lucy Durack (Wicked, 42nd Street), Kate Maree Hoolihan (Little Women, We Will Rock You) and Debra Byrne.