After being selected for the Free State U18 side at Craven Week and being selected in the SA schoolboys side in 2013, Viljoen signed a deal that saw him join the Western Province Academy.
He impressed early on at his time in the Western Cape and was named in the 2014 Super Rugby squad but a knee injury ruled him out for the rest of the season.
He made his Currie Cup debut later that year in the opening round fixture against the Sharks.
In March 2015 he was named in the South African U20s side for the World Rugby Under 20 Championship.
Viljoen was included in the Stormers 2017 Super Rugby squad and made his long-awaited debut in the opening round against the Bulls.
Viljoen had a fantastic debut Super Rugby season and featured in all 16 of the Stormers matches and was a key member of the Western Province squad that won the 2017 Currie Cup.
In July 2019, he signed a deal with Leicester Tigers.
(LS July 2, 2019)
|Grey College Bloemfontein
|2019 - present|
|South Africa U20's
|2014 - 2019|
|2017 - 2019|