Pignite once belonged to a Trainer named Shamus as a Tepig, who abandoned him after he lost to a Deerling in battle. Shamus was disappointed in Tepig and so, Tepig was tied to a post. When Don George tried to untie him, Tepig broke free of his bonds and began searching for his Trainer, but to no avail.
When Ash visited the Accumula Town Pokémon Battle Club in The Battle Club and Tepig's Choice!, Ash mistook Tepig for an Umbreon when watching a security tape of him stealing food from the nearby warehouse. In an attempt to capture the 'Umbreon', Ash then met Tepig for the first time when he was trying to eat some bait. He realized that Tepig was covered in soot and was unable to eat as there was a rope tied around his mouth, making him extremely hungry and very skinny. Initially, Tepig tried to run away, but after being cornered by Ash and having his rope removed and fed, he was carried back to the Battle Club by Ash. Later on, Tepig volunteered to help Ash retrieve his Pikachu from Team Rocket. Later, when Iris wanted to capture Tepig, he refused and decided he wanted to join Ash's team and Ash caught him in a Poké Ball.
Tepig fought for Ash during his Striaton Gym battle in Triple Leaders, Team Threats!, against Chili and his Pansear. Tepig's attacks didn't do much damage to Pansear, but Pansear managed to hit Tepig with powerful Fire Punch, Flamethrower and Dig attacks. One of Pansear's Dig attacks sent Tepig into the air. Ash then commanded him to dive into the hole that Pansear was in and he managed to bite Pansear's tail. Although Pansear threw Tepig onto the ground, he managed to get up and spin Pansear around, throwing him to the ground. He used Ember successfully and then knocked Pansear out with a powerful Tackle.
Tepig was revealed to be male in Snivy Plays Hard to Catch! when he battled a wild Snivy that would eventually be caught by Ash. Although he managed to use an Ember attack, he was hit by the Snivy's Attract and became infatuated with her, causing him to be recalled.
In The Battle According to Lenora!, he battled Lenora's Lillipup, which promptly used Roar to force Tepig back into his Poké Ball. After Lenora's Watchog defeated Oshawott, he fought Lillipup again and was defeated. In Rematch at the Nacrene Gym!, he trained alongside Ash at Don George's Battle Club. He ran on a treadmill and dodged black balls that symbolized Shadow Ball attacks. By training, Tepig became faster and stronger, and learned Flame Charge. Later on, he battled against Lenora's Herdier, which soon used Roar to force Tepig back into his Poké Ball again. After Watchog and Oshawott knocked each other out, Tepig battled Herdier again and won because of his faster, stronger attacks and his newly learned Flame Charge move.
He had his third Gym battle against the Bug-type Gym Leader Burgh in Battling For The Love of Bug-Types! and despite Ash planning to win with a type advantage, Burgh sent out a Dwebble which had its own type advantage. Even though Tepig tried his best, Dwebble's superior speed and powerful Rock-type moves got the better of Tepig which lead to his eventual defeat.
Tepig was later used in Ash and Trip's Third Battle! to battle Trip's Vanillite. Tepig defended himself from Vanillite's Ice-type attacks with Flame Charge but could not keep up with some of its faster moves and despite the type advantage, the match ended in a tie.
Tepig was used in Gotta Catch A Roggenrola! to battle Roggenrola after Oshawott was defeated, only to be defeated himself. He later helped Ash rescue all of the Roggenrola from the Team Rocket trio. He later had a rematch with Roggenrola and after a fierce battle, he weakened it enough for Ash to catch it.
In Evolution by Fire!, while eating with the other Pokémon in the Battle Club, Tepig recognized his previous Trainer, Shamus. Upon seeing him, Tepig happily ran over to Shamus, believing that he would be happy to see him. However, when Shamus threw Tepig at Ash and called him a useless Pokémon, he was very disheartened. Being angered by Shamus's actions, Ash accepted Shamus's challenge of a Double Battle, pitting Tepig against his former Trainer's Emboar and Heatmor the next day. That night Tepig sat alone outside the Battle Club and got very upset while recounting his abandonment. Snivy slapped him with Vine Whip and talked sense into him, as they were preparing for the battle in the morning. Despite Snivy's encouragement, when faced with battling his estranged Trainer, he froze up and was unable to launch any attacks. Though Tepig had thought that abandoning him was a very hard thing for Shamus to do, he was crushed when Shamus revealed he was relieved to get rid of him. However, after watching his friend Snivy take two powerful hits when she was distracted with encouraging him further, Tepig finally hit both of his opponents with a powerful Flame Charge. However, Emboar and Heatmor were able to take the attack and on Shamus's command launched a Flare Blitz/Fire Spin combination move. Making no attempt to dodge, Tepig was pushed out of the way of the attack by his partner Snivy, who took major damage and was knocked out. Tepig became as motivated as his Trainer and Snivy continued to show faith in him, as he evolved into Pignite. With his new power, Pignite used Fire Pledge, impressing both his former and current Trainer and dealing major damage to Emboar and Heatmor. With a final Flame Charge attack, Pignite was able to knock out both of his opponents. After the battle, Shamus talked to Pignite, saying he was impressed with his new power, and asked him to rejoin the team, but Pignite refused, scorching his previous Trainer's face with a Flamethrower and sending him running away in anger.
In Caution: Icy Battle Conditions!, Pignite battled Brycen's Cryogonal. The match started with Pignite's Flame Charge being blocked by Reflect and him being hit by fast Rapid Spin, unable to hit the speedy Cryogonal. After enduring Cryogonal's Frost Breath, Pignite was able to land a direct hit with Fire Pledge, stopping Cryogonal's Rapid Spin and knocking it out. Pignite next went up against Brycen's Beartic where his Flame Charge was stopped by Beartic's Brine. Pignite was soon knocked out after a powerful Icicle Crash and unavoidable Aerial Ace.
In Rocking the Virbank Gym! (Part 2), Ash sent out his Pignite as his fourth Pokémon during his Gym battle with Roxie, facing her Scolipede. Despite her part Bug-type Pokémon being at a type disadvantage against Fire-types, Roxie stood calm. Pignite started by trying a Flame Charge, which was blocked by Scolipede's Screech. The Megapede Pokémon next attacked with Sludge Bomb, which was also blocked by Pignite's Flamethrower, causing a big explosion and a cloud of smoke. Using the smoke to his advantage, Ash had Pignite use another Flame Charge, hitting Scolipede and dealing a lot of damage. As Pignite tried to finish the match with another Flamethrower, Scolipede dodged and used Toxic on Pignite, badly poisoning him. However, Pignite was able to go on and unleash a Fire Pledge on Scolipede, defeating it. Roxie then gave Pignite a Pecha Berry, curing him of the poison before sending out her strongest Pokémon, Garbodor. The Trash Heap Pokémon was able to use its extendable arms to dodge Pignite's Flame Charge before hitting the Fire Pig Pokémon with DoubleSlap and doing the same again to dodge a Flamethrower. Pignite then used Tackle on Garbodor's arm, causing it to fall over. Pignite was about to use Fire Pledge, but Garbodor extended its arm under his hand, preventing him from using the move, grabbing him, and tossing him to the floor. After getting hit by a few DoubleSlap attacks, Pignite was finally able to unleash his Fire Pledge attack, but Garbodor countered with a Hyper Beam, which went right through Fire Pledge and hit Pignite, knocking him out.
Pignite, as a Tepig, has been shown to not take losing very well, often getting sad when he loses, such as in A Rival Battle for Club Champ! where he fought and lost to Trip's Tranquill. This was shown again during Ash's battle against Lenora, the Gym Leader of the Nacrene Gym. He fought against her Lillipup and lost; he got depressed again, and did not even cheer up when Ash told him he did a good job. He also felt upset when he drew to Trip's Vanillite in Ash and Trip's Third Battle!, reacting the same way he does when he loses. However, in some cases, Tepig is happy to lose, but only in unofficial training battles, as seen in A Dragon Master's Path!. Otherwise, Tepig is a rather sweet Pokémon, always looking to please Ash in battle.
Tepig has shown multiple times that he is always trying to please Ash. Lenora confirms this in Rematch at the Nacrene Gym!, where she says that Tepig is trying very hard for Ash. This could be because Tepig's former Trainer abandoned him and out of fear that Ash will do the same, tries his best to prove he is worthy. Even though abandoned by his former Trainer, he was still happy to see him again in Evolution by Fire! and also didn't feel right battling against him. After his evolution, he lost all respect for Shamus as shown when Pignite used Flamethrower on his former Trainer and stayed loyal to Ash.
Ash sends out his Tepig against Leeku's Samurott in White—Victini and Zekrom. Tepig was having trouble handling Samurott as Samurott had both the advantage in being fully evolved and type. However, with Victini powering it up, Tepig defeated Samurott.