The former 'Awake' star will join Keanu Reeves and Willem Dafoe in the revenge film, according to Deadline.
Chad Stahelski and David Leitch's film is currently shooting in New York. It is not currently known what role Isaacs will play. He joins fellow supporting actors Alfie Allen and Michael Nyqvist.
Reeves stars as John Wick in the film, an ex-hitman who is being targeted by his old friend (Dafoe), after being hired by a crime boss.
Isaacs has also joined the cast of Brad Pitt's World War II thriller "Fury", alongside the likes of Shia LaBeouf, Logan Lerman and Michael Pena.