[14] On 6 July 2021, Firpo signed a four-year deal with Premier League club Leeds United for a fee of €15 million plus add-ons, with Barcelona reserving rights to 25% of his future sales.

[17] He scored his first goal for the club in Leeds’ 3–1 win in the FA Cup fourth round at the Wham Stadium over Accrington Stanley on 28 January 2023.

[19] Firpo did not feature regularly as part of new manager Daniel Farke’s back line for the 2023–24 season, making only four appearances in the first five months, only one of these as a starter.

[20] However, following Djed Spence's loan termination by Leeds, as well as an injury to Sam Byram, Firpo became the first-choice left-back in the new year, assisting 4 goals in three league games.

[21] On 31 August 2018, Junior was called up to the Spain under-21 team for two 2019 UEFA European Under-21 Championship qualifying matches against Albania and Northern Ireland.

[23] On 28 February 2024, Junior announced that he would represent the Dominican Republic going forward following talks with the national team's manager.