Tepig once belonged to another trainer who abandoned him after he lost to a Shikijika in battle. When Ash visited the Karakusa Pokémon Battle Club in BW004, 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 it 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. Initially, Tepig tried to run away, but after being cornered by Ash and having its rope removed, 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, it refused and decided it wanted to join Ash's team, and Ash caught him in a Poké Ball.
Tepig fought for Ash during his Sanyou Gym battle in BW005, against Pod and his Baoppu. Tepig's attacks didn't do much damage to Baoppu, but Baoppu managed to hit Tepig with Fire Punch, Flamethrower and Dig. One of Baoppu's Dig attack sent Tepig into the air. Ash then commanded him to dive into the hole that Baoppu was in and he managed to bite Baoppu's tail. Although Baoppu threw Tepig onto the ground, he managed to get up and spun Baoppu around, throwing him to the ground. He used Ember successfully, and then knocked Baoppu out with a powerful Tackle.
Tepig was revealed to be male in BW007 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 BW010, he was used to fight against Shooti's Hatooboo. Like Oshawott before him, he was defeated by two consecutive Aerial Aces due to Hatooboo's Super Luck ability.
In BW015, he battled Aloe's Yorterry, which promptly used Roar to force Tepig out. After Aloe's Miruhog defeated Oshawott, it fought Yorterry again and was defeated.