Brendan was born in Goldenrod City, Johto. He was a spontaneous little boy who couldn't wait to become a Trainer. However, when he was eight years old, an incident between him, a young girl and a wild Salamence resulted in his father losing his job and Brendan, realizing he had been too brutal fighting against the Salamence, promising to suppress his strength in battle.
On Brendan's sixteenth birthday, he and his mother moved to Littleroot Town, Hoenn. His father already moved there a few weeks prior after becoming the Petalburg CtyGym Leader. With his father coming home, Brendan ran away as he didn't want to face him as he didn't approve of Brendan's aspirations. After an incident with Professor Birch where Brendan fell from a small cliff, he met a young girl called May and battled with his first Pokémon, which he loaned from Professor Birch. After the two were safe and returned to Littleroot Town, May was revealed to be Professor Birch's daughter, and the Pokémon he borrowed was a Treecko, which Professor Birch then gave him as a thank you for helping him. Following this, Brendan returned home to find his father, who angrily scolded him, before Brendan told him that he would go on his journey and win all the Ribbons in Hoenn to prove to him that he can be the best Coordinator. Brendan then left his home for Petalburg City.
Soon after this, May returned and asked Brendan for a battle, which he declined. He explained why, and May realized that they had met before as she was the girl that he played with as a child. After getting to know each other a little more, May helps Brendan capture a Pokémon - a Wurmple. After a successful capture, May suggested they head to Petalburg City together, resulting in the two journeying together.
Arriving in Petalburg City, Brendan once again ran into his father as the Petalburg Gym, where he was also introduced to May's sickly friend Wally, who they then helped capture his first Pokémon. After Wally fainted during their capture attempt and taken back home, he and May tried to persuade Wally's parents to allow him to become a Trainer, however were unsuccessful. Afterwards, they left for Rustboro City for May's first Gym Battle.
Brendan was present once the group arrived at Slateport City, where they had their second encounter with Team Aqua. Intimidated by them, he failed to stop one of the members stealing an artifact from the Oceanic Museum, luckily, May was there to help. Brendan realized that he has to improve on his confidence, especially if he wants to be successful in Contests. He was scouted by Lisia outside of a Contest Hall in which he took part in his first Contest. Despite losing, Lisia continued to back him and told him she'd meet him in Fallarbor Town as she saw great potential in him. From that point on, Brendan focused more on his Contests.
When they finally arrived in Fallarbor Town, Brendan took part in his second set of Contests, taking part in the Normal Rank Clever and Normal Rank Beautiful Contests with Treecko and Wurmple respectively. He came first in his Clever Contest and third in his Beautiful Contest, catching the attention of a mysterious Trainer due to winning despite his lack of experience. Ecstatic with his win, Brendan became more determined than ever to focus on his Contests, but didn't tell anyone due to the current threats they faced.
After dealing with Team Aqua at Mt. Chimney, Brendan came to the conclusion he wouldn't be strong enough to face them again, despite confidence from May and Lexi, but once more kept this mostly to himself. In Contest Spotlight!, he took part in his third round of Contest against Shauna in four Contests. While he came in second in his first and won his second, he lost his third to a mysterious Trainer, who was soon revealed to be Wallace. After his Contest, Brendan introduced himself to Wallace and asked him to allow him to be his Mentor. Despite Wallace's initial refusal, he watched Brendan's fourth Contest, and despite him losing to Shauna, Wallace commended Brendan's attitude to losing and agreed for him to become his Apprentice, resulting in Brendan leaving, despite the shock and anger of Lexi and May respectively.
While away from the group, Brendan joined Wallace to Fallarbor Town once more, before taking part in more Contests while training under Wallace. He captured new Pokémon including Skitty, Zangoose and a Feebass who evolved into a Milotic who he captured to represent the Cute, Tough and Beautiful Contests respectively. He became more confident but after a conversation with Wallace discovered that he missed his friends. Brendan also was given a Mega Bracelet from Wallace, who revealed he saw the potential in him.
Brendan returned when the group reached Lilycove City, taking part in his Master Rank Contests. However, during his finale Contest, he discovered that the group was in danger with Team Aqua and left to help them, ultimately forfeiting his final Ribbon. He successfully helped them, before returning to Lilycove City and completed for his final Ribbon and won.
After he had finished his Contests, he decided to remain with the others and help them take down Team Aqua and Team Magma, along with support May after she decided to head to the Hoenn League. He also used this time to try and successfully inhibit Mega Evolution, after being given the Sceptilite by Wallace.