He progressed to their Under-19 and Under-21 sides, and made his first class debut in Western Province's match against the Leopards in the 2016 Currie Cup qualification series.

At the end of 2017, Jantjies was drafted into the squad of Welsh side Scarlets on their visit to South Africa during the 2017–18 Pro14 season,[4] and came on as a replacement in their match against the Cheetahs in Bloemfontein.

His constant game-changing performances got the interest from Paul Roos Gymnasium in Stellenbosch, where he started playing under 14 rugby for the D team.

At the age of 14, he undertook his first trip overseas where he represented a South African invitational side on a postseason rugby tour to Scotland in the UK.

[10] In July 2019, Jantjies made his debut for South Africa in their opening match of the 2019 Rugby Championship against Australia in Johannesburg, scoring twice in a 35–17 win.