Oscar Ingemar Kristoffer Vilhelmsson was born on October 2, 2003 in Åsa and made his IFK Göteborg debut in the 2019 season, which was also the debut season of team mate Giannis Anestis. Vilhelmsson was part of IFK Göteborg's youth program before making his debute with the first team, and is as a result of that regarded by the club as a home-grown player. At 15 years, 10 months and 19 days, on August 22, 2019, he took part his first competetive game against BK Astrio in a Svenska cupen game that ended 4–0. He has as of today spent two seasons with the IFK Göteborgs first team, and during his career he has played in 7 first team games and scored 1 goals. Out of these 7 first team games, 3 were Allsvenskan games.
Oscar Vilhelmsson is with his 3 Allsvenskan games number
415 on the list of those who have competed in most Allsvenskan games for IFK Göteborg. In the 2019/20 season he had a part in IFK Göteborg winning the Swedish Cup. Vilhelmsson is as of today, October 30, 2020, an active IFK Göteborg player. He currently holds the individual club records of Yngste goalsskytt (15 år, 10 månader, 19 dagar) and Yngste spelare i Svenska cupen (15 år, 10 månader, 19 dagar). 17 year old Vilhelmsson is today, October 30, 2020, an active player for IFK Göteborg.