In 2002, Mackintosh joined the company of the Stratford Shakespeare Festival appearing as Freddy Eynesford-Hill in My Fair Lady.
He has also played Robert in The Drowsy Chaperone (Vancouver), Phil Davis in White Christmas (Halifax), Prince Charming in Ross Petty's Cinderella (Toronto), Gustl in The Land of Smiles, Rapunzel’s Prince in Into the Woods (Avon Theatre), and Algernon Moncrieff in Earnest, the Importance of Being (Toronto Operetta Theatre).
He made his Broadway debut in 2011 in the role of George Banks in Mary Poppins at the New Amsterdam Theater in New York City.
He played Nicky Goldberg in the independent film Songbird directed by Alex Boothby, Don Giovanni in Avenging Angelo (Sylvester Stallone/Warner Bros.), Young Anwyn Noble in Prince Charming (Martin Short/Hallmark) and Bob Kachler in Rad (Lori Loughlin/Taliafilm).
On 5 May 2014, he started a one-week limited engagement as the Phantom between Hugh Panaro's departure and Norm Lewis' arrival.