Poli was Red's first Pokémon. It is unknown when Red received Poli or if he caught Poli. Flashbacks show Red as a young child with the Pokémon, before the first chapter of Pokémon Adventures. As a child, Red would have drowned, if it wasn't for Poli evolving from a Poliwag to a Poliwhirl, who brought him up to the surface. As a Poliwhirl, he was Red's main battling Pokémon despite him making other catches such as a Nidorino with it, though his defeat against a wild Mew is what causes Red to rethink his hubris in thinking there was no one in the world who could best him, and Blue's Charmander later injured it badly.
Along with Pika and Saur, he is one of Red's most frequently used Pokémon. He was also principal in Red's battle for the Boulder Badge, though his ample amount of uncured damage from past battles prevented him and Saur from competing in the final match against Brock. He is not seen battling much afterward, only for carrying Misty's Staryu out of Mt. Moon, and in an attempt to demobilize a wild Fearow which had survived Pika's Thunder, forcing Poli to freeze it to incapacitate it.
In Buzz Off, Electabuzz!, Poli evolves into Poliwrath to save Red from drowning again after he falls off the S.S. Anne, having been thrown off deck by Lt. Surge before. At first, it was believed that Poli somehow evolved without a Water Stone. However, in the Yellow arc, it is explained that he touched one of the four evolutionary stones speculated to be at the bottom of Vermilion Harbor.
At the Pokémon League, Poli and Pika helped Saur defeat Blue's Charizard in a brilliant strategy to have Poli's water vapor and Pika's electric energy create a thundercloud that struck a vine shot and wrapped around it by the Venusaur.
With Red missing for most of the Yellow chapter, Poli was not seen in battle except in a match against Bruno's Hitmonchan in which he seemed to hold the upper hand until Hitmonchan's Thunder Punch attacks eventually deplete Poli's health, finishing him. He also participates in Red's rematch against the Elite Four, where he is again beaten by a powerful Machamp in yet another ruse: the water that leaked from it when being stopped allowed Vee to maneuver behind his Pokémon by surprise, allowing it to evolve into a Jolteon and defeat them with a massive Pin Missile.
During the Gold, Silver & Crystal arc, Red does not carry Poli on his team with him, enabling him to use both Green's Blastoise and Blue's Charizard. This is a reference to Red's team in Pokémon Gold and Silver.
Poli's Damp Ability combined with Deoxys's use of Skill Swap enabled Red to counter Carr's exploding Forretress in the FireRed & LeafGreen arc. He also defeated Carr's Steelix, showing an impressive feat of hurling the megaton monster away. However, once Deoxys arrived and launched its Psycho Boost attack, Poli and the rest of its teammates are nearly killed after shielding Red from the blast, which shatters Red's confidence.
During the Emerald arc, Poli joined forces with Gold's Polibo while battling against the Guile Hideout. After saving Emerald and his Dusclops from Jirachi's Doom Desire attack, Poli used Double Team to confuse Guile Hideout so that Polibo could get a chance to sneak closer and attack. Although Guile Hideout tried to send his Walrein and Masquerain to attack the Tadpole and Frog Pokémon, they rather simply threw them away and attacked Guile Hideout directly, breaking his armor.