The actor, who played Ryan in the 2013 series of the hit series Peaky Blinders, was also known for his time on the hit Irish soap Fair City as Robbie.
His agent confirmed his death, reports The Sun.
Shiels worked on internationally-acclaimed television shows and films including Batman Begins, Veronica Guerin, Intermission, The Clinic, and Capital Letters for which he was nominated for an IFTA for Best Actor in 2004.
The TV star started out as electrician but changed direction in the early 90s and studied at the Gaiety School of Acting.
Tributes are already flooding in to a “remarkable” actor who was “loved by all”.
Comedian and fellow Fair City actor who played Cathal Spillane, Eric Lalor said: “Absolutely stunned and heartbroken to hear of the death of Karl Shiels.
“A hugely gifted actor and a really great friend, I will miss him so much. Thinking of his gorgeous family, may he Rest In Peace.”
Director of Copper Face Jacks: The Musical has said that Karl will be “sorely missed”.
He said: “Shocking news to hear that Karl Shiels has passed away. He was a big supporter of @HelixPanto. Irish Theatre will sorely miss him.”
She said in a statement: “Karl was a uniquely talented individual, simultaneously intense, lighthearted, funny, sharp witted, outspoken and intensely powerful as an actor, director and artistic director of the Theatre Upstairs — where he was such a support and mentor for young writers, actors and directors — and of his own company Semper Fi before that.
His agent Lisa Richard confirmed that Shiels had passed away on Sunday.
“Karl was a remarkable force in Irish theatre and hugely loved and respected by all who worked with him.
“Our hearts are broken but today our thoughts are with his partner Laura and his family, his children and their mother Dearbhla and his many close friends among whom we count ourselves lucky to have been for so many years.”
This story was originally published in The Sun and is reprinted with permission.