Born in Spain to Ecuadorian parents, he represented England at youth international level before making his senior Ecuador debut in October 2021.

A youth product of Charlton Athletic and Benfica, Sarmiento signed for the academy of Premier League side Brighton & Hove Albion on 2 July 2021.

[3] He made his professional career debut on 22 September, coming on as a 69th-minute substitute for injured Alexis Mac Allister in the 2–0 home victory over Swansea City in the third round of the EFL Cup.

[7] He made his Premier League debut on 27 November, coming on as an 82nd-minute substitute replacing Jakub Moder in the goalless draw at home against Leeds United.

[8] Sarmiento made his first Premier League start four days later, where he ultimately played just 13 minutes due to an injury in which he was replaced, in the eventual 1–1 away draw at West Ham United.

"[15] Sarmiento made his first Premier League start of the season on 3 January 2023, where he helped set up Evan Ferguson's goal in the 4–1 away win over Everton.

[30] On 14 November, Sarmiento was named in Ecuador's 26-man squad for the 2022 FIFA World Cup alongside Brighton teammates Pervis Estupiñán and Moisés Caicedo.