The former Emmerdale and Casualty actor will replace the outgoing Diane Keen, who will leave the soap after nearly 10 years next week.
Kelsey will play confident, divorced ex-army captain Howard Bellamy, who is said to have a highly different and strict outlook on working life in comparison to Keen's Julia Parsons.
The actor said: "Diane Keen has left some big shoes for me to fill, so it's lucky I have size 13 feet!
"The producers and writers have created a gem of a character for me to play in Howard, so it's great to go to work every day and be able to sink your teeth into the next scenario Howard finds himself tackling…and it being Doctors that could be anything!"
Julia will be involved in a car crash with love interest Martin Millar later this week, leaving viewers to wonder whether they will survive the accident or not.
Series producers Peter Lloyd and Mike Hobson added: "We're so sorry to see Di go. After a wonderful run as Julia she has been an unwavering support and advocate for the show and we wish her the best of luck in her next projects."
Kelsey will make his first appearance as Howard Bellamy in Doctors on Monday, May 28.