Ji-soo Kim began his football journey representing Bucheon Donggok Elementary School before he moved to the youth team of Seongnam.

While plying his trade at Seongnam, he became the youngest player in the K League, South Korea’s top division, aged 17, and the first player in the league to sign a contract on semi-professional terms.

He competed in the 2023 U20 Asian Cup and 2023 U20 World Cup. South Korea reached the semi-final of the latter competition, beating France and Nigeria on their way before losing to Italy.

Ji-soo played in 19 K-League matches for Seongnam before his move to Brentford B in July 2023.

A month later he earned his first call-up to the senior South Korea squad, boss Jurgen Klinsmann selecting him for friendlies against Wales and Saudi Arabia.

The young defender was a consistent performer for Brentford B during the 2023/24 season, earning recognition from first-team head coach Thomas Frank who selected him on the bench eight times across the campaign.

Prior to the 2024/25 season, it was announced that Ji-soo would be promoted to Brentford’s first-team squad.