He attended Hoërskool Kempton Park and was called up to represent the Falcons at the 2012 Under-18 Craven Week tournament held in Port Elizabeth.
He played rugby for university side UJ, and was included in their Varsity Cup squad for the 2015 and 2016 events.
Oosthuizen was included in the Eastern Province Kings squad for the 2016 Currie Cup Premier Division, and named on the bench for their second match of the competition against the Blue Bulls in Pretoria.
[5] He made his first class debut during the match, coming on for three separate spells during the match; he came on as a temporary blood replacement for both Sebastian Ferreira and Tazz Fuzani in the first half before coming on as a tactical substitution for the final eight minutes.
[6] Oosthuizen joined Golden Lions Grand Challenge side Pirates prior to the 2017 season.