Johan (Aranos) Coetzee was born on 14 March 1988 in Windhoek and went to primary school in Aranos before moving to South Africa to attend Hoër Landbouskool Boland in Paarl. He was selected to represent Western Province at the 2006 Academy Week. He was part of a South African team participating in the Under-18 Africa Cup.

After high school, Coetzee moved to Potchefstroom, where he represented the Leopards U21s in the 2008 and 2009 Under-21 Provincial Championships.

Coetzee played Varsity Cup rugby for NWU Pukke during the 2010 Varsity Cup competition. He made eight appearances as he helped Pukke reach the semi-finals of the competition for the third consecutive season, where they lost to eventual champions Maties.

Coetzee made his first-class debut on 9 July 2010 for the Leopards, playing off the bench in a 13–43 defeat to the Golden Lions in Phokeng in the 2010 Currie Cup Premier Division.

After the 2010 Currie Cup Premier Division, Coetzee moved to France and joined Top 14 side Racing Métro (2010-'12). Coetzee then moved to Brive (2012-'15) and played in 62 matches for them.

He returned to South Africa to join the Toyota Cheetahs for the 2015 Currie Cup season. He missed most of the tournament due to his involvement with Namibia at the 2015 Rugby World Cup.

He made his test debut for his country of birth, Namibia, on 6 June 2015 in their 2015 Africa Cup match against Tunisia in Nabeul. Coetzee was in a 50-man Namibian training squad before the 2015 Rugby World Cup.

The Toyota Cheetahs gave him the SuperRugby player of the year award in 2017. Coetzee's name is one of the first to be written down when a team gets selected, and he was also part of the Namibia Nation side at the 2019 Rugby World Cup in Japan.

He played in his hundredth match for the Toyota Cheetahs on 21 August 2021.

Coetzee is on loan for Bath Rugby in England from 1 August until 15 November 2022. "Aranos is still under contract at the Toyota Cheetahs and will provide a backup while Bath's tighthead is rehabilitating from injury. The Free State Cheetahs is glad to allow him the opportunity to play in the English Premiership," said Free State Cheetahs' CEO, Ross van Reenen.

Aranos has played 109 games for the Toyota Cheetahs since he made his debut for the side on 12 March 2016 in a Vodacom Super Rugby match against the Sunwolves of Japan in Singapore. He has 25 caps for the Namibian national team.

The Toyota Cheetahs' next matches will be in the Toyota Challenge in October 2022. Coetzee will be back in the Toyota Cheetah camp before the first EPCR match in early December.