Mario Mario along with his younger brother Luigi Mario are plumbers from Brooklyn, New York who are on the verge of being run out of business due to the mafia-operated Scapelli Construction Company led by Anthony Scapelli.
When Luigi falls in love with an NYU student named Daisy, Mario tries to muster Luigi's courage to ask her out. They went to an Italian restaurant in which Mario brings his girlfriend Daniella along as a double date. After Luigi and Daisy witness the Scapelli sabotaging the bridge by leaving the water pipes open, Mario and Luigi manage to stop it but are knocked unconscious by Iggy and Spike, where they take Daisy.
Mario and Luigi wake up, and upon hearing Daisy's scream, they follow it by heading deeper to the caves, only to discover an interdimensional portal in which Daisy seems to be trapped. The two brothers jump in where they enter into a dystopian parallel world where a human-like race evolved from Dinosaurs, called Dinohatten.
They were being under arrest by police who were sent by the other world's evil and feared dictator, King Koopa who was descended from the T-Rex, who wanted a rock that was on Daisy's neck but was taken by Luigi when he tried to get her out of the portal but was taken by Big Bertha. The Mario Bros. escape Koopa when Koopa was about to use a machine to transform them into Goombas but was inturned used on him as he slowly began to transform back to his dinosaur formed.
They escaped the policed by using one of their cars, and almost fell off a cliff until they were saved by a huge fungus, which caught them right when they were about to crash to where they wind up in a desert. The next morning, they were confronted by Iggy and Spike who appeared to be a lot smarter after Koopa used to the same machine on them to increase their intelligence in finding the Mario Bros, but it eventually caused them to turn on Koopa and join forces with the Mario Bros. After Mario's attempt to seduce Bertha to get the rock from her, but was taken again by Lena (Koopa's girlfriend), the two eventually find Daisy with a little help from Toad, who was a guitarist that was transformed into a Goomba. Mario manages to save Daniella and a few other girls who were kidnapped by Iggy and Spike after mistaken each of them for being Daisy who happens to be revealed as a princess whom Koopa believe to merge the two words, together, with the rock fragment that Koopa wanted It's also revealed that the fungus that saved Mario and Luigi was Daisy's father.
Mario went face to face with Koopa, as the two worlds began to merge, but Luigi and Daisy manage to remove the stone which causes the two worlds to be separated once again after Lena was killed once she used it to merge the two worlds. The Mario Bros. manage to face Koopa and use their devolution guns to fire at him, and blasted him with a Bob-omb. This caused Koopa to devolved into his Tyrannosaurus form, before becoming primordial slime. With Koopa defeated, the two worlds are no longer merge, and Daisy's father was turned back to normal and reclaimed his thrown. Luigi is reluctant to leave Daisy, and he and Mario returned home to Brooklyn. Three weeks later, the Mario Bros. were getting ready for dinner as the anchorman on the news stated that due to their bravery they should be called the "Super Mario Bros." They immediately get a surprise visit from Daisy who asks them for help on their next mission to which they all agree to join.
- It has been reported that Bob Hoskins openly despised the movie he was in when he got the part as both he and John Leguizamo were drunk during most of the filming.
- Before Bob Hoskins was cast as Mario, Danny DeVito, Dustin Hoffman, Bruno Kirby, Cheech Martin, and John Goodman were all considered for the role of Mario.