Gibson, who played Martin Riggs in the previous four films will take over the director's chair from the late Richard Donner.
Gibson first starred in the franchise in 1987, alongside Danny Glover.
Speaking at the event in London, Gibson said: "[Donner] was developing the screenplay and he got pretty far along with it. And he said to me one day, 'Listen kid, if I kick the bucket you will do it.' And I said: 'Shut up.' But he did indeed pass away."
He then went on to confirm: "But he did ask me to do it and at the time I didn’t say anything. He said it to his wife and to the studio and the producer. So I will be directing the fifth one."
Reports from Deadline suggest that he is in talks to both direct and star in the fifth outing for the franchise.
The streaming service HBO Max will develop the film.
Before Donner passed away, he confirmed that 'Lethal Weapon 5' would be the last in the franchise.
"It’s both my privilege and duty to put it to bed. It’s exciting, actually… Hahaha! It’s the last one, I’ll promise you that."
It's unknown when the project will get going. Gibson has a number of films in the works, including 'John Wick' spinoff 'The Continental'.