Stuart, 31, said the title had been 15 years in the winning, and he was honoured to have gained the same title as "the Austrian Oak" Schwarzenegger, who was crowned amateur Mr Universe in 1967, and won the professional title in 1968, 1969 and 1970.
He said: "It's 15 years of working out in the gym and giving up nice food and going out and it's all been worthwhile.
"To be on the same list of winners as Arnold Schwarzenegger is really unbelievable. Watching Terminator movies growing up, then you get to be on the same list as Arnie, it's overwhelming."
Competitors are judged on the symmetry, proportions and the size and clarity of each muscle group. Stuart, who has previously won the titles of Mr World and Mr Britain, said the latest win meant he could turn professional.
He said: "It's just mind-blowing really, to be able to call yourself Mr Universe. They can't take that away from me now. To be able to finally be the top of what you do is such an amazing feeling, I don't think there are words to describe it."
Stuart's focus on the challenges still to come meant his celebrations were not extravagant, and he is already back in the gym and watching his diet.
He said: "I think consistency over the years I have steadily got better and improved.
"I'll have a bit of time off really now, and a bit of normality in my life, before starting my assault on the professional league."