He played for the at all youth levels, representing them at the 2007 Under-13 Craven Week, the 2010 Under-16 Grant Khomo Week and in the 2012 Under-18 Craven Week. His performances in the latter tournament earned him inclusion in the South African Schools team that played against France, Wales and England in August 2012. Petersen scored a try in each of those matches to ensure that the South African remained unbeaten in the series. He was included in the squad for the 2013 IRB Junior World Championship, but failed to recover from a hamstring injury in time and was replaced by Jesse Kriel. He got a second opportunity the following year when he was included in the South Africa Under-20 side for the 2014 IRB Junior World Championship held in New Zealand. He opened his scoring in that competition just half an hour into the opening match against Scotland, helping his side to a 61–5 victory. He started their second match of the competition, where South Africa beat the hosts and four-time winners New Zealand 33–24, and scored a try in the final minute of their last match of the pool stages to secure a 21–8 victory over Samoa. Petersen contributed largely to South Africa once again beating New Zealand in the semi-final of the competition, this time winning 32–25 and he started his fifth consecutive match of the competition in the final against England; however, this time he finished on the losing side, with England winning the match 21–20 to be crowned champions for the second consecutive year.
After finishing school at the end of 2012, Petersen signed a three-year contract with the Kings despite interest from several other teams. A few months later – and without any first class matches under his belt – he was named in the squad for the 2013 Super Rugby season. He made his first class debut in the Southern Kings' first ever Super Rugby game against the on 23 February 2013. He also scored the Kings' first ever try in Super Rugby...as well as their second during the second half, earning him a Man of the Match award. He started a total of eight matches for the Kings during the season, scoring further tries in their matches against the and a consolation try in their 72–10 defeat to the. He only made his debut for provincial side the after eight Super Rugby appearances, coming on as a substitute in their 37–21 2013 Currie Cup First Division victory over the in Welkom. A further two appearances followed that season, as well as one for the side during the 2013 Under-21 Provincial Championship. He also helped out the side during their title run-in in the 2013 Under-19 Provincial Championship series. He scored two tries try for them in their 45–30 semi-final win over, a further one in the final against the in a 56–40 win and scored yet another one in their promotion play-off match against, winning 27–20 to help the team win promotion to Group A. In 2014, Petersen made two appearances for the Eastern Province Kings during the 2014 Vodacom Cup competition and scored a try in their match against the. Upon his return from international duty at the 2014 IRB Junior World Championship, he was included in their squad for the 2014 Currie Cup Premier Division season. He was not involved in any matches for the first team at all, instead representing the side in the 2014 Under-21 Provincial Championship. He scored seven tries in seven appearances as the side won the Under-21 competition for the third consecutive season and also scored two tries in their promotion play-off match against to help them secure promotion to Group A for 2015.
Cheetahs
In July 2014, it was widely reported that Petersen signed a contract to play for the during the 2015 Super Rugby season, while still being available for the during the 2015 Currie Cup Premier Division. However, Kings CEO Charl Crous said that, while they would assist their players in gaining Super Rugby experience, no deal was in place with the Cheetahs for a Petersen loan for 2015. It was then revealed that Petersen signed a three-year contract with the for 2015–17 and he was included in the ' wider training group prior to the 2015 Super Rugby season.
In 2016, Petersen was included in a South Africa 'A' squad that played a two-match series against a touring England Saxons team. He didn't play in their first match in Bloemfontein, but started the second match of the series, scoring two tries in a 26–29 defeat in George.
