The 43-year-old star will play Jason Taylor, who is S&M-loving billionaire Christian Grey's bodyguard and head of his security team, in the film adaptation of EL James' best-selling novel, according to Deadline.
The 'Pacific Rim' star will appear alongside Jamie Dornan, who plays male lead Christian Grey, and Dakota Johnson, who has been cast as his love interest Anastasia Steele.
Dornan and Johnson are currently preparing for the film's steamy sex scenes and 'The Fall' actor, who is replacing Charlie Hunnam in the film, previously confessed he isn't afraid of tackling the graphic moments.
Martini, who is a trained theatre, film and TV actor, has previously been cast as former FBI agent Frank Stevens on hit TV series 'Revenge' and a US Navy SEAL commander in 2013 action thriller 'Captain Phillips'.