The actor, who was a semi-finalist in the 2013 series of Strictly Come Dancing, appears alongside another former Casualty actor Ian Kelsey in The Shawshank Redemption.
It can be seen at Milton Keynes Theatre from Monday, November 16, to Saturday, November 21.
Despite protests of his innocence, Andy Dufresne is handed a double life sentence for the brutal murder of his wife and her lover.
Incarcerated at the notorious Shawshank facility, he quickly learns that no one can survive alone, but strikes up an unlikely friendship with the prison fixer Red, and things take a turn for the better.
Patrick said: “I play the character of Red in the film and the story is all about the friendship between these two characters of Andy Dufresne and Red.
“The show is based more on the original Stephen King story which I really liked rather than the film.
“I have to explain to people that I am playing a character Morgan Freeman played in the film rather than doing an impersonation of him.
“We have been getting very good feedback from people although it has been interesting, the reaction varies depending on which audience we are at. Some people have laughed at bits that other audiences haven’t.
“There have been some audiences who have applauded enthusiastically and others who were more muted because they were so caught up in the story.
“In a way, the ultimate challenge for all of us on the production is to make sure the audience is drawn into that world and are moved by that world.”
Patrick, who worked for eight years on Casualty across two separate spells, has been most recently seen on screen in Strictly Come Dancing.
He added: “In a way, I was sad to not reach the final of the show. I didn’t get to do to the Argentine tango but did manage everything else. But because I came back for the group dance the week after I never missed out.
“It is something that I really enjoyed doing. If I am going to go out to a night club, I will go to dance rather than to drink.
“As an actor, I think you look for new challenges and something that is a little bit different and then this opportunity came along and really loved doing it.
“There are a couple of things that I have planned at the moment. But nothing is confirmed just yet. I’ve just started working on Mount Pleasant for Sky which has been fun.”
Tickets for The Shawshank Redemption cost from £11. To book call the box office on 0844 871 7652 or visit www.atgtickets.co.uk/miltonkeynes.