The British actor has reprised the role for the eagerly-awaited sci-fi movie and has given fans of the franchise a small idea about what they can expect to see in the new film, which is released later this year.
Speaking to Access Hollywood, John teased: "It's gonna be lots of fighting for Finn.
"A lot of running, a lot of shooting. It's a really dark mission."
And despite this being his second 'Star Wars' movie, John admitted he's still not fully adjusted to the attention that comes with appearing in the iconic series.
He explained: "I think my ears have now gotten used to it, but the experience of it all ... you never get used to it.
"I mean, people you don't know are just screaming and rightly so. Doing amazing things with this franchise and this movie, so it's a nice way of showing love to the fans and them showing love to you, too. So it's cool."
Earlier this month, meanwhile, director Rian Johnson revealed he had the "time of his life" making 'Star Wars: The Last Jedi'.
The Hollywood movie-maker said he relished directing the film because the sci-fi series means so much to him.
He said: "My friends, whenever I talk to them recently ... ask me what the experience was like, I always come back and say I had the time of my life making this movie.
"Part of that is what 'Star Wars' means to me, and what it means to a lot of us."