A veteran of 19 Tests, Samu is now locked in through 2023, meaning he's positioned to be a key part of Australia's World Cup tilt next year.
The 30-year-old said there was minimal temptation to leave the nation's capital.
"Me and my family are really settled here, and the opportunity to stay another year - I didn't think twice," he told reporters.
"I'm stoked and grateful for the opportunity to stay another year. This club means a lot to me and my family."
Wallabies coach Dave Rennie said he was thrilled the Samu deal was inked.
"His athleticism and speed are a point of difference across the backrow and we think his best footy lies ahead of him in the gold jersey," he said.
It comes as the Brumbies approach their Super Rugby Pacific round-two clash against Fijian Drua knowing they need to improve on their first-round effort.
They struggled at the lineout, turned the ball over 19 times, spent almost the entire first half in defence and needed a miracle last-minute try to wrestle a 29-23 win against the Western Force, and captain Allan Alaalatoa stressed the importance of a better showing in round two.
"There were a lot of learnings from last week ... we made too many mistakes and what we do know is if we do the same thing tomorrow they'll probably capitalise on that.
"We need to improve a lot of areas ... in defence and then mistakes.
"We turned over the ball too many times, that's gonna happen but if it does we need to be better at reacting and moving onto the next job."
The Fijians showed glimpses against the Waratahs in round one but eventually could not handle their pace, falling 40-10 in a one-sided affair.
Round one match-winner Lachie Lonergan and his brother Ryan join the Brumbies' starting lineup, with the latter to start at scrumhalf with Wallaby Nic White shifted to the bench.
For Drua, Kaliopasi Uluilakepa will debut at prop as will Ratu Rotuisolia at lock, while Baden Kerr shifts from five eighth to fullback.
Turning the contest into a physical battle and not letting Drua get rolling and throw the ball around will be crucial, Alaalatoa said.
"We've got to dominate contact up front, that's the biggest thing for us," he said.
"We've watched two games from them, but we saw two different things.
"They're so good in attack when you give them opportunity. We've got to be very precise with how we give them the ball and make sure our defence is a little bit better."
10°C