Anton Frondell was born in Trangsund, Sweden, and started playing senior-level hockey at age 16 for Djurgardens IF in the second-tier HockeyAllsvenskan during the 2022-2023 season. In 2021-2022, he played 32 games (between three tiers) and scored 32 goals and assisted on 28 tallies. During the 2023-2024 season, Frondell played for six teams total, including three international squads. He finished the season playing in 70 games total, scoring 44 goals and 38 assists. He competed in the 2024 Under-18 Five Nations Tournament as a 16-year-old, leading Sweden in goals and beating Team USA for first place in the event.