A versatile young player, Scarles joined West Ham at eleven and has worked his way through the age groups. His progress at the Academy of Football also saw him receive England caps at U15, U16, U17 and U18 levels.

Playing for the West Ham United U18s at just 16 in the 2021/22 season, Scarles would make 25 appearances in all competitions, scoring once. His immense campaign would conclude with the signing of his Scholarship deal in June 2022.

The following season Scarles made his first team debut in a 3-0 UEFA Conference League victory over FCSB on 3 November 2022, with the wing-back playing a starring role. He was rewarded with his first professional contract on his seventeenth birthday. His season would only get better, playing an instrumental role in the U18s historic FA Youth Cup and Premier League South double, while also making 16 appearances for the U21s.

In 2023/24, Scarles made 19 appearances for the U21s, scoring two goals and registering five assists. He also travelled with the first team seven times across all competitions before his season ended prematurely in February with a back injury.

However, he returned to fitness in summer 2024, travelled with the first-team squad on their pre-season tour of Florida, and signed a new long-term contract on 2 October 2024.

Scarles made his Premier League debut on 16 December 2024, coming on as a second-half substitute in a 1-1 draw against AFC Bournemouth. In his FA Cup debut on 10 January 2025, Scarles delivered a man of the match performance as Aston Villa edged past the Hammers in a 2-1 defeat away to Aston Villa.

His full Premier League debut would come a month later at Arsenal, in another man of the match performance as the Hammers won their second consecutive league game at the Emirates Stadium thanks to a 44th minute strike from Jarrod Bowen.

Scarles was named Mark Noble Hammer of the Year in May 2025.