Youth and Varsity Rugby

Willemse was included in the Eastern Province Kings squad at the 2010 Under-18 Academy Week and also played for the Eastern Province U19 team in the Under-19 Provincial Championship competition in the same year. In 2011, he also represented them at the Craven Week competition.

In 2013, he played Varsity Cup rugby with the UCT Ikey Tigers, scoring three tries in six starts.

Western Province / Stormers

He was called up to the Western Province Vodacom Cup squad at the conclusion of the Varsity Cup competition and made his first class debut on 13 April 2013 against Argentina side Pampas XV^[2] and made four appearances in the competition.

He made his Currie Cup debut a few months later when he came off the substitutes' bench for their match against Sharks following Tiaan Liebenberg's late withdrawal through injury.^[3][4]

In 2014, he was called up into the Stormers squad for their 2014 Super Rugby match against the Sharks, following Deon Fourie's late withdrawal through injury.^[5]

UK

On 25 March 2019, Willemse traveled to Scotland to sign for Edinburgh in the Pro14 on a two-year deal from the 2019-20 season.^[6] Following his release from Edinburgh, he signed for English club London Irish in the Premiership Rugby from the 2021-22 season.^[7]

Representative rugby

In 2013, he was included in the South Africa Under-20 squad for the 2013 IRB Junior World Championship. He made three substitute appearance – against the USA (scoring two tries),^[8] England,^[9] and France.^[10]