Valenciennes Masuaku came through the youth system of
Valenciennes. He made his
Ligue 1 debut on the opening game of the
2013–14 season on 10 August 2013 against
Toulouse. He was substituted after 75 minutes for
Tongo Doumbia. On 29 January 2014 Masuaku scored his first competitive goal for Valenciennes in a 2–1 away defeat against
Marseille.
Olympiacos In July 2014, Masuaku signed for
Olympiacos. He made his
Super League debut against
Niki Volos, and in his third league match he provided two assists against
OFI in a 3–0 home win. Three days later he made his debut and scored in the
UEFA Champions League competition against
Atlético Madrid in a 3–2 home win. In April and May 2015, interest from
Roma,
Internazionale and
Juventus was reported. His agent, Roger Henrotay, however stated a renewal of Masuaku's contract was on the cards. In July, a reported €4 million offer for Masuaku including former Olympiacos midfielder
Giannis Fetfatzidis from
Genoa was rejected by the club.
West Ham United On 8 August 2016, Masuaku joined
West Ham United on a four-year contract for a £6.2 million fee. He made his West Ham debut in a 2–1 away defeat to
Chelsea on 15 August 2016. Masuaku admitted that he found his Premier League debut very tough due to the pace and physicality of the league. He scored his first goal for West Ham in an
EFL Cup tie against
Bolton Wanderers on 19 September 2017. In the FA Cup fourth round game against
Wigan Athletic on 27 January 2018, Masuaku was sent off for spitting at Wigan's
Nick Powell following a challenge. It was the first sending-off of Masuaku's career. Masuaku apologised for the sending off, saying the incident was "totally unacceptable and out of character". He received a six match ban for the offence. In July 2019, having played 75 times for West Ham, Masuaku signed a contract extension with the club until 2024 with an option to further extend the contract for two years. On 4 December 2021, Masuaku scored the winning goal in a 3–2 victory over defending
UEFA Champions League winners
Chelsea. The goal, a mishit cross that caught out Chelsea goalkeeper
Edouard Mendy at his near post, was his only
Premier League goal.
Beşiktaş On 2 August 2022, Masuaku joined Turkish team
Beşiktaş on a season long loan with an option to buy in 2023. On 17 April 2023, Masuaku completed a permanent transfer to
Beşiktaş. The fee was undisclosed by the clubs but was reported by some sources to be in the region of £2million. On 30 June 2025, Beşiktaş announced Masuaku's departure from the club.
Sunderland On 10 August 2025, Masuaku signed a two-year contract with Premier League club
Sunderland. On 27 January 2026, Masuaku joined
Lens in
Ligue 1, where he already played as a youth, on loan until the end of the 2025–26 season. ==International career==