Fiennes will receive a British Film Institute Fellowship in recognition of "a singular career" that has blended arthouse dramas and mainstream hits.
Fiennes - who plays evil Lord Voldemort in "Harry Potter" series - said he was "extremely honored and delighted" by the award.
Fiennes' directorial debut, an adaptation of Shakespeare's "Coriolanus," will screen during the Oct. 12-27 festival.
Cronenberg, the director of "Videodrome," "The Fly" and "Crash," will receive the same honor in recognition of films "exploring the darker impulses and inner lives of his characters."
Cronenberg said he was thrilled to be the first Canadian to receive the award.
"British cinema has been a potent inspiration for me, and to be associated with this particular group of filmmakers is tremendously exhilarating," he said.
The pair are due to receive the prizes at the London Film Festival awards on Oct. 26.
Previous BFI fellows include "Slumdog Millionaire" director Danny Boyle and actor John Hurt.
Organizers also announced a shortlist for the festival's best film prize. The nine finalists, selected by artistic director Sandra Hebron, include French silent movie "The Artist"; Aleksandr Sokurov's Venice Film festival winner "Faust"; British director Steve McQueen's body- and soul-baring "Shame"; and Lynne Ramsay's high school massacre drama "We Need to Talk About Kevin."
Alexander Payne's "The Descendants," which stars George Clooney as a neglectful father of two daughters whose wife falls into a coma, is the only American film among the finalists.
The winner will be chosen by a panel that includes "Shakespeare in Love" director John Madden, actress Gillian Anderson and artist/director Sam Taylor Wood.