Sio was named in the Wallabies 31-man Squad to take on the British and Irish Lions in their three test series. Despite being named in the squad, he was allowed to play in the Brumbies game against the Lions, performing admirably, to become the first Australian provincial side to defeat the Lions in 42 years.[citation needed]
Sio made his run-on debut at loosehead prop against the All Blacks during the winning final of the 2015 Rugby Championship, after a pair of impressive cameos from the reserves bench against South Africa and Argentina. Sio was named in the Wallabies 31-man squad for the 2015 Rugby World Cup, where he supplanted most-capped Wallabies prop James Slipper as the Wallabies first choice loosehead. He currently is now a regular in the Wallabies starting XV at loosehead prop.[citation needed]
He is son of the former Samoan prop David Sio, who played in the 1991 Rugby World Cup (Samoa played against Scotland in that tournament at the time of Scott's birth and he was named in recognition of the occasion)[3] and also the cousin of up and coming player Fereti Sa'aga who has also represented Australia on the Junior stage.
On 17 August 2022, Sio would travel to England to join Exeter Chiefs in the Premiership Rugby on a long-term deal from the 2022-23 season.[4]