The veteran Hollywood star, who will be best remembered for playing the cantankerous father in 'Frasier' and for starring alongside John Cusack in the teen movie 'Say Anything', died at the age of 77 in a Chicago hospice following a short illness.
John was born in Blackpool in England and was the seventh of eight children of Margaret and Reg, a baker.
A latecomer to the acting world, was almost 40 before he decided on a career in Hollywood and made his first film appearance in 1980.
He was encourage to pursue a career in acting after meeting John Malkovich in a Chicago acting class, who urged him to join the Steppenwolf theatre company.
He went on to appear in many hit films such as 'Moonstruck' with Cher, 'In The Line of Fire' with Clint Eastwood, and the Coen Brother's 'Barton Fink' and'The Hudsucker Proxy' with Paul Newman.
He also starred in Roman Polanski's 'Frantic', 'Reality Bites', 'The Russia House', 'Tin Men' and 'The American President'.
But it's 'Frasier and Say Anything' that he will be best remembered for. After 'Frasier' ended, Mahoney was approached with other TV series offers, but turned them down because he wanted to return to the theater, which he considers his "home".
He even went on to visit Ireland and worked in theatre in both Dublin and Galway.
"I'm very proud to have 'Frasier' as my television legacy,' Mahoney told the Associated Press in 2014. "I've done a lot of good television myself. But still I think nothing can quite compare to 'Frasier.''
John Cusack, who starred with John in 'Say Anything', was one of the first to pay tribute on Twitter this morning to his co-star friend.
When he first heard the news, he simply wrote "fuck" on Twitter and followed that up by asking if it could be a "hoax".
But when the news finally sinked in, John wrote a series of moving tweets in his honour. In one, he said: "He always said - it took him a long time to find out what he loved - and he loved performing - he was so happy to be there - he made everyone around him better and happier each day - blessed to know him."
He was the glue that held that film together-:) great great artist https://t.co/fhuFC2ghtE— John Cusack (@johncusack) February 6, 2018
He always said - it took him a long time to find out what he loved - and he loved performing - he was so happy to be there - he made everyone around him better and happier each day - blessed to know him https://t.co/d7UKnCzB6c— John Cusack (@johncusack) February 6, 2018