Sapsford described his contract extension on Thursday as a "no-brainer", with the winger also enjoying the option of a third season.
He credited Lonergan, who is having a stellar season with the Brumbies, for his on-field influence that has steered the Canberrans to third place on the Super Rugby Pacific ladder.
Sapsford says while Lonergan has been playing well for a long time, his off-field impact was "impeccable".
"The thing that I'm most grateful about coming to this club is the person that I'm becoming," Sapsford said.
"I'm still not where I want to be, but I've come a long way from 2021 off the field and on the field, and that's due to the boys in here.
"Ryan's one of them. He's very black and white. He knows what's right and what's wrong. He's just a really solid leader.
"He's always been a standout player since I've been here, and I'm just super pumped for him to see the experience and skill set that he has flowing into his games."
Lonergan currently leads the competition on points (57), having orchestrated tries, scoring his own and registering a mammoth number of passes.
It's only strengthened the 27-year-old's case for another Wallabies call-up after making his international debut last year.
Sapsford has played 58 games for the side, with his contributions earning him a call-up for the Australia A team.
"When I was 20, I set myself a goal to play Super Rugby," the 30-year-old Sapsford said.
"I was super proud when I played 50 games last year. I couldn't really believe it at the time.
"I feel like I've still got more to give, and I've got high goals as well."
The Brumbies are having a much-needed bye week after going down 30-28 to bitter rivals Waratahs last Friday night.
However, they have suffered a blow to their outside back depth after Kye Oates dislocated his ankle and underwent surgery.
The speedster will miss the remainder of the season.
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