Mario works as a grocer alongside his brother Luigi in their store. One night, while playing a video game, he sees Princess Peach emerge from the television, pleading for help as she flees King Koopa. Mario attempts to defend her but is overpowered, and Koopa kidnaps Peach, returning through the screen. The only trace left is a small green necklace dropped during the struggle.

The next day, Mario remains troubled by the event and the necklace. Luigi recognizes the gem from a book and believes it can lead them to the Mushroom Kingdom, a land rumored to hold great treasure. Their pursuit of a dog-like creature named Kibidango, who steals the necklace, leads them into a warp pipe. They emerge in the Mushroom Kingdom, where a mushroom hermit reveals he summoned them. He explains that the kingdom is under attack by King Koopa, who is turning citizens into inanimate objects after Princess Peach rejected his marriage proposal. A prophecy identifies Mario and Luigi as the ones destined to defeat Koopa. The hermit advises that they must find three mystical Power-Ups: a Super Mushroom, a Fire Flower, and a Starman.

Mario becomes determined to rescue Peach and save the kingdom, while Luigi is primarily motivated by the prospect of gold coins. Their journey is guided by Kibidango. Mario shows persistence and honor. He acquires the Super Mushroom, granting increased size and strength, and the Fire Flower, allowing him to shoot bouncing fireballs. He uses these to overcome obstacles and enemies such as Koopa Troopas, Bullet Bills, and Buzzy Beetles.

Mario’s problem-solving skills are evident as he navigates dangerous situations, escaping a garden infested with Piranha Plants, avoiding attacks from a Lakitu, and breaking out of a prison cell. He eventually retrieves the final Power-Up, the Starman, from underwater after Luigi accidentally drops it. Using a sunken ship, Mario, Luigi, and Kibidango travel to Koopa’s castle.

Mario arrives at the wedding ceremony and confronts King Koopa. Initially, the Power-Ups are not enough, and Mario is nearly defeated. He uses the Starman, which grants invulnerability and enhanced power, allowing him to overpower and defeat Koopa. The defeat breaks Koopa’s spell, restoring the Mushroom Kingdom and its transformed citizens.

Afterward, Mario returns Peach’s necklace. This causes Kibidango to revert to his true form, Prince Haru of the Flower Kingdom. He explains he is Peach’s fiancé and was transformed into a dog by Koopa. Mario is heartbroken to learn Peach is to marry Haru but accepts the situation and wishes them well. Mario and Luigi promise to return if needed before journeying home.

In a post-credits scene, King Koopa and his minions are shown working at the brothers’ grocery store as part of their punishment.

Mario is occasionally considered overweight and has black hair, dark brown eyes, and a round face. He typically wears a red shirt, blue overalls with yellow buttons, a red cap with an “M” insignia, white gloves, and brown boots.

His personality is marked by a strong sense of justice and determination, especially when motivated to rescue Peach and save the kingdom. He can be impulsive and easily distracted, such as by food during a critical battle. Mario also shows deep emotional investment, as seen in his heartbreak over Peach’s engagement, though he ultimately prioritizes her happiness.