AZ in 2020|268x268px Koopmeiners grew up in
Castricum,
North Holland, and took his first steps in football as a youth player for the local club, Vitesse '22. In 2009, he joined the
AZ youth academy at under-12 level. 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 the
2016–17 season, reaching promotion to the
Eerste Divisie. On 18 August 2017, Koopmeiners made his professional debut for Jong AZ in a 3–1 away win over
FC Den Bosch. He made his first team-debut on 1 October, coming on as a substitute for
Alireza Jahanbakhsh for the final 30 minutes of a 4–0 home loss to
Feyenoord. At the end of the
2017–18 season, AZ ended in third place, and thereby qualified for
Europa League. In his first professional season, he made 26 league appearances in which he scored one goal. On 1 March 2020, Koopmeiners played a 70-metre pass to set up
Oussama Idrissi for AZ's second goal in a 2–0 win against
Ajax which put his side level on points with Ajax. During the
2019–20 AZ Alkmaar season Koopmeiners scored 16 goals in all competitions in 42 appearances, helping his side finish second in the
Eredivisie on goal difference behind the Champions
AFC Ajax. He scored his first goal of the
2020–21 season against
Viktoria Plzen on 26 August 2020 in the
UEFA Champions League qualifier 3–1 victory. On 14 January 2021, Koopmeiners scored two goals, including an audacious backheel flick, to help his side clinch an 3–1 away victory against
PSV Eindhoven.
Atalanta On 30 August 2021, Koopmeiners signed for
Serie A club
Atalanta for a reported fee of €12 million. He made his debut on 11 September in the home match against
Fiorentina, as a late substitute for
Matteo Pessina. On 1 September 2022, Koopmeiners scored a
hat-trick in a 3–1 Serie A victory over
Torino. On 22 May 2024, he started in Atalanta's 3–0 victory over German champions
Bayer Leverkusen in the
2024 UEFA Europa League final.
Juventus On 28 August 2024, Koopmeiners moved to fellow Serie A club
Juventus, signing a five-year deal. 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". On 1 September 2024, Koopmeiners made his first
Juventus appearance in a 0–0 draw with
AS Roma, replacing
Juan Cabal at half-time. ==International career==