Having represented the Netherlands at various youth levels, Koopmeiners was called up to the senior team's preliminaryUEFA Nations League squad in August 2020.[3] He was later part of their squad for the2022 FIFA World Cup.
Koopmeiners grew up inCastricum,North Holland, and took his first steps in football as a youth player for the local club, Vitesse '22.[4] In 2009, he joined theAZ youth academy at under-12 level.[5] He eventually progressed through the ranks, and as part of the club's reserve team,Jong AZ, he became champion of the Dutch third division in the2016–17 season, reaching promotion to theEerste Divisie.[6]
On 18 August 2017, Koopmeiners made his professional debut for Jong AZ in a 3–1 away win overFC Den Bosch.[7] He made his first team-debut on 1 October, coming on as a substitute forAlireza Jahanbakhsh for the final 30 minutes of a 4–0 home loss toFeyenoord.[8] At the end of the2017–18 season, AZ ended in third place, and thereby qualified forEuropa League. In his first professional season, he made 26 league appearances in which he scored one goal.[9]
On 1 March 2020, Koopmeiners played a 70-metre pass to set upOussama Idrissi for AZ's second goal in a 2–0 win againstAjax which put his side level on points with Ajax.[10] During the2019–20 AZ Alkmaar season Koopmeiners scored 16 goals in all competitions in 42 appearances,[11] helping his side finish second in theEredivisie on goal difference behind the ChampionsAFC Ajax.[12]
He scored his first goal of the2020–21 season againstViktoria Plzen on 26 August 2020 in theUEFA Champions League qualifier 3–1 victory.[13] On 14 January 2021, Koopmeiners scored two goals, including an audacious backheel flick, to help his side clinch an 3–1 away victory againstPSV Eindhoven.[14]
On 30 August 2021, Koopmeiners signed forSerie A clubAtalanta for a reported fee of €12 million.[15] He made his debut on 11 September in the home match againstFiorentina, as a late substitute forMatteo Pessina.[16]
On 1 September 2022, Koopmeiners scored ahat-trick in a 3–1 Serie A victory overTorino.[17]
On 28 August 2024, Koopmeiners moved to fellow Serie A clubJuventus, signing a five-year deal.[19] The transfer fee paid to Atalanta was €51.3 million plus €3.4 million in "ancillary costs" as well as a further €6 million "upon the achievement of further performance objectives".[20]
On 1 September 2024, Koopmeiners made his firstJuventus appearance in a 0–0 draw withAS Roma, replacingJuan Cabal at half-time.[21]
On 19 August 2020, Koopmeiners was called up to the seniorNetherlands national team by caretaker managerDwight Lodeweges in the preliminary squad for theUEFA Nations League fixtures againstPoland andItaly.[3] The same year in October, he debuted in a friendly match againstMexico.[24] He made his competitive debut in a2022 FIFA World Cup qualification againstTurkey on 7 September 2021, contributing with an assist in a 6–1 victory.[25] Koopmeiners scored his first senior national team goal in aUEFA Nations League match againstWales on 8 June 2022.[26] In the2022 World Cup quarter-final againstArgentina, known as theBattle of Lusail, Koopmeiners assisted former AZ teammateWout Weghorst with a clever free-kick routine in the 11th minute of stoppage time to send the fixture to extra time. He then scored his penalty in the subsequentshoot-out but could not stop the Netherlands from being eliminated 4–3.[27]
On 29 May 2024, Koopmeiners was named in the Netherlands' squad forUEFA Euro 2024.[28] However, he was forced to withdraw from the tournament squad after sustaining an injury during the warm-up for a friendly match againstIceland on 10 June 2024.[29]