The actor has signed up for the role of Adrian 'Fletch' Fletcher, a new nurse for Holby's Emergency Department.
Walkinshaw is leaving his role as Waterloo Road's Jez Diamond and will begin filming at Casualty's new home in Cardiff later this month.
Speaking of his character Fletch, Walkinshaw commented: "He's the ultimate cheeky chappy - the kind of entertaining bloke you'd really want to go down the pub and have a laugh with, whether you're male or female.
"He's into football, rugby, beer and beautiful women - only to flirt with and admire, though - he's a devoted family man which just makes him all the more attractive. Personally, I can't wait to get to know him better myself!"
Casualty's executive producer Johnathan Young commented: "We're absolutely thrilled to welcome Alex to the Casualty team. He's brings bags of talent, a wealth of experience and a cheeky sense of humour to rival Fletch's!"
Fletch originally trained as a mechanic, but ended up losing his business. When his wife Keila went into labour with their third child and found herself in Holby's ED, Fletch saw the hard work of the nursing staff and decided it was the career for him.
By arriving back in the ED, Fletch is returning to the birthplace of his daughter and his inspiration.
Casualty airs Fletch's first episode in June, which will see Lloyd (Michael Obiora) assigned as his mentor.
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