And he's clearly off to a good start.
While first five-eighths shoulder a large degree of decision-making in any team, Barrett's swift elevation speaks volumes of his rapid progress over the last two years and, indeed, his growing importance to this team.
"We had a good meeting before we left and Reado set out the expectations that he wanted for the week and the tour," All Blacks coach Steve Hansen explained. "Beauden is the vice-captain so he'll lead and drive the team from a captain's point of view this week. Whether he plays or not we'll wait and see but he's the head leader on the ground at the moment.
"He's played over 50 tests now so he understands what test matches are all about. He's been driving the team for quite some time."
The reality is the Barbarians at Twickenham probably presents a good chance for Lima Sopoaga to shake off his disappointing performance against the Wallabies in Brisbane. The opening match on Sunday (NZT) should be open and expansive, and comes with little pressure in terms of the result. It could, therefore, allow Sopoaga to regain confidence with successive starts at No 10, with Barrett potentially coming off the bench at either first-five or fullback.
"In Kieran's absence Steve gave me the heads up yesterday. I'm really looking forward to the week ahead," Barrett said of the leadership duty. "I don't know where that fits into the match-day XV or 23 but I'll just continue to do what I do."
In Sam Cane the All Blacks already have someone who has captained this team twice - against Namibia and Italy. Between Cane and Barrett, the role can easily be shared.
"It's pretty special," Cane said. "It's something you don't really think about a lot as a player when you set your goals about what you want to try and achieve. Most of the time leadership is something you grow into overtime.
"A lot of times after training in huddles Kieran has the final say so that might fall on Beauden's shoulders a little bit more but he often chips in anyway because he has a big say in how our attack runs and how we play the game. Maybe there's a wee bit more voice than normal."