The 30-year-old has spent six months out after dislocating his left shoulder in last year's World Cup.
He will become the sixth Brumbies player to make a century of appearances, after George Gregan (136 games), Stephen Larkham (116), Jeremy Paul (112), Bill Young (100) and George Smith, who cracked the ton last month.
"This match against the Chiefs was always identified as my comeback game, I've done the rehab and now I can't wait to get out there," Mortlock said.
"We've got a great young squad at the moment and the enthusiasm they bring to the squad is infectious. I feel very privileged to be able to work with these exceptional young players to help shape the future of the Brumbies.
"I feel very fortunate to have been able to play at this level for so long. I've loved being part of the Brumbies and I've always enjoyed - and will continue to enjoy - playing my football here.
"When you look at the guys who have played 100 games for the Brumbies, they stand out as some of the greatest players to ever play for the club and for the Wallabies, so to be considered in that company is a real honour."
Coach Laurie Fisher was full of praise for his returning captain.
"We're very pleased to have Stirling back in the squad," he said.
"He's been a very influential player in the success of the Brumbies over the past decade.
"During his career, Stirling has developed into a world-class leader. He's a player that other players listen to and he's a player that inspires his team mates with his lead-by-example style of play.
"He's provided Brumbies supporters with some memorable moments over the past 11 years and I'd like to think they will get out to Canberra Stadium on Friday night and help celebrate this terrific achievement."
Mortlock, in his fifth season as Brumbies captain, is the all-time record points scorer for the team with 825 and trails the province's all-time try-scorer Joe Roff (57) by just nine tries.