Lee, 32, became a household name in 2006 when he took part in Andrew Lloyd Webber’s TV talent competition Any Dream Will Do, winning the starring role in the West End revival of Joseph and the Amazing Technicolor Dream Coat.
In 2011 the stage star made his TV acting debut as a guest in Casualty, where he played teaching assistant Harry Timms, who witnessed his boss, Emma (Pooky Quesnel), slap a student.
“I’m thrilled to be joining Casualty. I really enjoyed my guest appearance in 2011, but this will be a completely different challenge,” he said.
He added: “When I first read about the character, Lofty, I didn’t imagine I would be in the frame to play him. I am hoping he will charm audiences and they will get behind him. I can’t wait to get started and to learn all of the medical jargon!”
Lee will start filming at BBC Cymru Wales’ Roath Lock Studios in coming months, and viewers will be able to see him on screen for the first time in early 2014.
Speaking to What’s on TV at the time Lee said this about his first small screen role: “It’s been a dream of mine to act in film and TV for a long time – and it’s been well worth the wait because I had the most amazing experience!”
He added: “It’s funny in 2006 I was going to stop musical shows completely to study acting. Then a TV show called Any Dream Will Do came up and I auditioned… And my whole life changed completely!”
Meanwhile, Footballers’ Wives star Jamie Davis is due to join Casualty later this series, as laidback hospital porter, Max – stepbrother to nurse Robyn.