Hailing from Houghton-le-Spring, Sonny joined the Academy with the Under-14 age group.

In October 2021, the dynamic forward was called up for the England U17s qualifiers in Belarus and featured three times.

In August 2022, aged just 17, he was invited by Chris Wilder to train with the first-team in pre-season.

Sonny made his debut for Boro against Barnsley in the EFL Cup, featuring from the start in a 1-0 defeat to the Tykes.

On 11 March 2023, Finch marked his league debut with a substitute appearance in the 3-1 win against Swansea. He featured two further times in the remainder of the season as Boro reached the play-offs. 

In the same season, Sonny was called up by England’s U18s for games against Switzerland, Belgium and Croatia. The attacker scored a goal in the first minute of the game against Switzerland to open his account for the national team.

In the 2023/24 season Sonny made the squad for Michael Carrick’s side on four occasions, and came on as a substitute in a 2-0 win against Swansea.

As well as featuring for the first-team, Sonny played seven games in the PL2, with the forward's most impressive game coming against Manchester United, when he scored two goals and got an assist in a 3-2 win.