Sio, 27, has made 55 Test appearances for Australia since his debut in 2013, a year after he played his first game for the Brumbies.
He will remain in Australia and with the Brumbies until at least the end of 2022 after his new deal was announced on Wednesday.
"I'm super excited to re-sign. I've obviously been at the club for a long time and I've seen a lot of what we're trying to grow," Sio said in a statement.