Born in Newtownabbey, Northern Ireland, in September 2000, Kofi Balmer began his football career with Ballymena United, scoring on his NIFL Premiership debut for the side at 16-years-old in a 1-1 draw with Coleraine in 2017. 

The defender would feature in 27 matches in the 2017/18 campaign, followed by 28 in the 2018/19 season; a year which also saw him named the Ulster Young Football of The Year.

Balmer joined Larne in 2021 and played 43 matches in all competitions in a little over a season with the side, along with six in the UEFA Europa Conference League qualifying stages.

His efforts earned a transfer to Premier League team Crystal Palace where, under the guidance of Patrick Vieira, he earned a place in a Premier League matchday squad on three occasions and made regular showings for the Eagles U21s. 

A loan to Sky Bet League One side Port Vale then followed in July 2023, where he made 16 appearances in all competitions, before another loan switch to then-League Two side AFC Wimbledon in January 2024.

Balmer signed for Motherwell in June 2024 and would score for the Steelmen on his debut a month later in a Scottish League Cup fixture. He made 24 appearances in all competitions last season, including 20 in the Scottish Premiership, and has featured nine times so far this campaign for Motherwell in all competitions. 

At international level, Balmer was a frequent inclusion in the Northern Ireland U21s and U19s, captaining both teams during his team at the respective age levels, and was first called into the senior set-up in September 2025. He was again called up for full international duty in August 2025.