Arsenal Obi started his career in Denmark with powerhouse team
Copenhagen, often playing up one or two age groups with the 05's and 06's. He eventually moved to England when he was 13 because of his mother's new employment, going on to join the academy of
Arsenal. He progressed through the club's youth ranks, establishing himself as a prolific goal-scorer, and was promoted to the under-18 side at the age of fifteen. In his first start for the under-18 side, he scored a
hat-trick in a 4–0 win against
Southampton on 23 September 2023, earning comparisons to Nigerian international striker
Victor Osimhen in Danish media. The following month Obi made his first appearance for the club's under-21 side, while still fifteen. He continued his meteoric rise at Arsenal in early November 2023, being called up by first-team manager
Mikel Arteta to join the senior side for training. Obi made international headlines on 18 November 2023, scoring ten goals as Arsenal beat
Liverpool 14–3 at under-16 level. On 27 April 2024, Obi made headlines once again, scoring seven goals for Arsenal in their 9–0 win against
Norwich City, taking his tally up to 24 goals in his previous seven games for Arsenal's under-18s. On 29 July 2024, Obi announced his departure from Arsenal on his Instagram account.
Manchester United Linked with a move to fellow
Premier League club
Manchester United in the summer of 2024, the deal was concluded at the end of September. The following month, Obi was named by English newspaper
The Guardian as one of the best players born in 2007 worldwide. On his first start, Obi scored a hat-trick in a 6–0 Under-18s win over
Nottingham Forest. Obi was named in a senior squad for the first time on 16 February 2025, making his senior debut as a 90th-minute substitute for
Casemiro in a 1–0 league defeat at
Tottenham Hotspur. Obi was named in the starting line-up for United's game against
Brentford on 4 May, the first senior start of his career; at the age of , he became the youngest player to start a Premier League game for United, surpassing
Mason Greenwood's previous record of . On 30 May 2025, Obi scored his first two senior goals for United in a 3–1 friendly win against
Hong Kong. ==International career==