*Club domestic league appearances and goals, correct as of 10:43, 14 January 2024 (UTC) ‡ National team caps and goals, correct as of 21:45, 4 March 2023 (UTC)
Hartjes is a youth product of Spijkenisse and Sparta Rotterdam, and joined the youth academy of Feyenoord in 2015.[3] He signed his first professional contract with the club on 18 July 2020.[4]
On 15 August 2022, Hartjes joined Eerste Divisie club Roda JC Kerkrade on a season-long loan.[7] He made his debut for the club as a starter in defensive midfield in a 3–0 away win in the league over FC Den Bosch after a hat-trick from former Feyenoord teammate Dylan Vente.[8][9] On 18 October, Hartjes scored his first competitive goal at senior level, providing the 2–2 equaliser in a KNVB Cup match against Heracles Almelo.[10] Despite keeping Roda's hopes of advancement alive, Hartjes would later miss the decisive penalty in the shootout, knocking the club out of the cup competition.[11] He scored his first league goal on 30 January 2023 in a 2–1 away defeat to league leaders PEC Zwolle.[12]
Excelsior (loan)
On 10 July 2023, Hartjes joined Eredivisie side Excelsior on loan for the remainder of the season.[13]
Excelsior
On 26 July 2024, Hartjes permanently joined Excelsior on a three year contract.[14]