The 30-year-old Lealiifano was named as co-captain for the side last year in what turned out to be a mostly symbolic role as he recovered from a bone marrow transplant after being diagnosed with leukaemia in 2016.
He returned for the Brumbies in their 35-16 playoff loss to the Wellington Hurricanes last season before he signed a short-term contract with Ulster and played for the side in the Pro 14 competition before returning to Canberra.
"Both Sam and Christian did a good job as co-captains last season showing excellent leadership both on and off the field," Brumbies coach Dan McKellar said in a statement on Thursday.
"In reappointing them for the new season we are maintaining our continuity of leadership and I am certain that they will both have a big impact in the role during the year.
"It's important for our captains to have the respect of their team mates and both Sam and Christian definitely have that."
McKellar, who replaced Stephen Larkham as Brumbies coach after former Wallabies flyhalf joined the national side coaching setup fulltime, said Lealiifano had benefited from his time in Ireland.
"Having that game-time under his belt will be a big bonus heading into the Super Rugby season and he has hit the ground running at training," McKellar said of the 19-test Wallabies utility back.
The Brumbies, who won the Australian conference last year but were bundled out in the first round of the playoffs by the Hurricanes, open their season against the Sunwolves in Tokyo on Feb. 24.
(Reporting by Greg Stutchbury in Wellington; Editing by Amlan Chakraborty)
