Balcombe came through the youth ranks at Griffin Park to join the original Brentford B squad in 2016, playing over 50 times under various Head Coaches.

An England youngster too, Balcombe started his Three Lions journey as an Under-18 player before he progressed through to Under-21 level. In 2017, he was part of the England squad that won the Toulon Tournament.

Making it into the matchday squad for Fulham in the Sky Bet Championship and then Notts County in the Emirates FA Cup, Ellery had a short loan spell at Boreham Wood in 2018. That move was cut short by a knee injury he sustained on international duty.

Ellery was present in Nyon, UEFA Headquarters, in December 2018 to collect England’s Fair Play Award from the U19 Championships in Finland the previous summer. While there, he also helped conduct the European draw for the U19 tournament in Northern Ireland.

Following his time with England at the Toulon Tournament in summer 2019, he started another loan spell with Danish side Viborg FF. That deal lasted until January 2020, when he was recalled by Brentford due to a back injury.

On 6 January 2021, Balcombe joined League One club Doncaster Rovers on loan until the end of the 2020–21 season. He finished his spell with 17 appearances.

On 29 June 2021, Balcombe joined League One club Burton Albion on loan for the duration of the 2021–22 season.