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.
"It's really cool to be part of the youth's next progression as well. I've seen that Noah Lolesio and Len Ikitau have re-signed too so it's great to be part of their journey as well.
"It's a special town. I've spent eight years of my life in Canberra and you get pretty close with the fans, and I really appreciate that so I'm looking forward to a couple more years.
"Winning the World Cup with the Wallabies is the goal this year so we need to recognise the steps to get there. We just had a camp in Brisbane and it was great to get the vibe and what we want to do moving forward."
"I have loved every minute of my time at the Brumbies ....It’s a unique family atmosphere that is recognised throughout the rugby World and I love being part of it.”#BrumbiesFamilyhttps://t.co/7SLg6RL4ky
— Plus500 Brumbies (@BrumbiesRugby) May 21, 2019
Wallabies coach Michael Cheika was thrilled with Sio's decision to re-sign.
"I'm really pleased for Scott and for Australian rugby that he's committed long term. He's already given so much to each of the teams he plays in but he's still got plenty left to give," he said.
"One thing that stands out with Scott is his commitment to the cause. He's always committed to being a better person, a better player and contributing to a better team."
Photo Getty Images. Caption: Wallabies star Scott Sio