Calem Nieuwenhof (born 17 February 2001), is an Australian professional footballer who plays as a defensive midfielder for Scottish Premiership club Heart of Midlothian.

[3] On 19 November 2020, Nieuwenhof made his professional first-team debut, as an injury replacement player,[4] in a 2–1 home loss against Shanghai SIPG in the AFC Champions League.

[6] On 2 January 2021, he started and scored on his league debut, a long-shot outside of the 18 yard, in a 2–1 win against Wellington Phoenix at Sky Stadium.

[18] During the league campaign, Nieuwenhof remained a starter for the club despite a stacked experienced midfield that featured Oliver Bozanic, Romain Amalfitano and former teammate Miloš Ninković.

[19] He later formed a partnership with former Premier League player Morgan Schneiderlin, who arrived in January on loan, and mentored Nieuwenhof from his experiences in the top divisions of Europe.

[30] As the first summer signing for the club, he joins alongside compatriots, Kye Rowles, Nathaniel Atkinson and Cameron Devlin.

I played with Oli Bozanic last year and he spoke so highly of his time here [...] I actually came to a Hearts game back in 2018 and I remember vividly how much passion there was.

[34] In March 2023, following his immense form at club level, Nieuwenhof received his first call-up to the Australia U23 training camp, in preparations, for the Paris 2024 Olympics qualification.

[35] On 24 March, he made his debut for the Olyroos, starting the match against the Switzerland U20 side, before being substituted for Ryan Teague, in a narrow 1–0 defeat at Stadio Comunale Bellinzona.

[2] He considers both Miloš Ninković and Luke Brattan as mentors, with the midfielders helping him settle with the first team during his first years in Sydney FC.