Hailing from the London borough of Lambeth, Isaiah joined Boro from Tooting & Mitcham in 2019 after helping his former side to a sixth-place finish in the Isthmian South Central Division.

Initially linking up with our under-23 side, he was named Premier League 2 Player of the Month in December that year.

In the January transfer window, Isaiah joined Scottish side St Johnstone on loan until the end of the season before returning to the Riverside as a first-team squad member under Neil Warnock.

After penning a new contract, the youngster made his English professional debut as a late substitute away to Brentford in the FA Cup in January 2021 and crossed the border again to join Scottish Championship side Queen of the South on loan for the remainder of the 2020/21 season.

Isaiah made his first league appearance for Boro on the opening day of the 2021/22 campaign and provided the assist for Marc Bola's late equaliser against Fulham. 

He was rewarded with his first start against Blackpool in the Carabao Cup a few days later, and then his first league start versus Bristol City, where he laid on another assist for Uche Ikpeazu's opener. 

As a reward for his stellar performances, Isaiah signed a new contract in November 2021, which runs until 2025. 

He was named Players' Player of the Year and Young Player of the Year at the end of the 2021/22 season.

After his impressive season in 2021/22, the wide player got 34 appearances under his belt the following year and finished the campaign with three goals and five assists.

The 2023/24 campaign was another stand out season. The wide player scored eight goals and tallied up four assists in 35 league appearances in the Championship.

Isaiah got an impressive brace in a 4-0 win at home to Preston while also getting a goal and an assist in our 4-0 win at the Stadium of Light.

In the 2023/24 season the London-born winger made his 100th appearance in the red of Middlesbrough, having established himself an integral part of the squad.

He was called up to represent Guyana for the first time in September 2024.