The 26-year-old, who made 20 first-class appearances for Durham since joining the club in 2015, has been an established part of DCCC’s pace attack and a prominent figure in the dressing room.
Ireland’s recently-awarded Test status meant that McCarthy, who has played in 29 white ball fixtures for his country and taken 57 wickets, would have been classed as an overseas player in English domestic cricket and would therefore limit his appearances for Durham.
“It’s been an absolute pleasure to be part of such an amazing club for the past four years and I will certainly miss it,” McCarthy said.
“I’ve had an unbelievable experience and I would like to thank everyone at Durham for such a positive experience.
“Emirates Riverside is a very special place and I have made some fantastic friends here; I am extremely proud to have a played a part in the history of DCCC.”
Durham County Cricket Club, Head Coach, Jon Lewis, added: “We are going to miss Barry in the changing room, pitch, and around the club.
“He’s got a great opportunity with Ireland to demonstrate his talent on the world stage and show what he can do.
“On behalf of the whole coaching staff, players and everyone at the club, I'd like to wish Barry every success in the future.”
©Cricket World 2018