The 34-year-old called time on his rugby career earlier this year, after 17 years in the game and 77 caps for England.
Haskell will compete for American MMA promotion Bellator having spent years in and out of London Shootfighters gym.
Bellator star Michael Venom Page has helped Haskell hone his skills, but a debut isn’t expected until 2020.
Haskell will feature in the heavyweight division and will make his bow in the Bellator cage in the new year, although a specific date is yet to be decided.
After launching a European fight series this year, Bellator will have a host of UK-based shows that Haskell could feature on in 2020.
The former flanker trained in MMA throughout his rugby career to help with fitness and has spoken at length about his love for the sport.
Haskell made a short statement on social media after the news of his shock move into MMA was announced, saying: ‘Soooooooo! This is happening, Bellator.
‘The journey begins and I could not be more excited. Shootfighters is now my new home.’
Bellator have a wealth of decorated heavyweight veterans in their ranks, including Russian legend Fedor Emelianenko, with Ryan Bader the current champion of the division.
Haskell played in two World Cups for England and won three Six Nations before hanging up his boots last May.