Alaalatoa will take the reins from Sam Carter and Christian Lealiifano, who both moved overseas at the end of the 2019 season.
The 24-year-old was widely considered to be one of the frontrunners for the position, having been a mainstay of the leadership group in recent seasons and one of the most consistent on-field performers.
Alaalatoa has set a strong example away from rugby as well, with his work pursuing a criminology degree and his on-field form earning him the 2019 RUPA Medal for Excellence.
The tighthead prop has played all his Super Rugby with the Brumbies and has already re-signed with the team to stay in Canberra until at least 2023.
“It’s a huge honour and privilege to be named as the captain of the Brumbies," Alaalatoa said.
“The Brumbies were the club who first gave me an opportunity to realise my dream of playing professional rugby and I’ll be doing everything I can to repay that opportunity as a leader of the club.
“There is such a great history of leadership at the organisation and there are so many great leaders within the squad as well, who will support me and help drive our standards both on and off the field this year and beyond.”
Brumbies coach Dan McKellar said Alaalatoa would follow in a line of high-profile leaders in the group.
“Allan’s been at the club for a long time now and has developed into a really strong leader in both the way he plays and how he holds himself amongst the group.”
“He’s a key figure for us on and off the field and will be well supported by the vice-captains and senior leaders at the club.
“The Brumbies have a long history of strong leaders and I congratulate him on being named the side’s captain for 2020.”
Joe Powell, Tom Cusack and Locky McCaffrey will be the Brumbies' vice-captains in 2020.