Williams acknowledged the challenge his new role at the Blues represents when saying: "It's an extremely tough job and I respect that. There have been many great leaders of this team before me and my job along with the team is to strengthen the strong traditions that the Blues have."
He is clearly comfortable making his opinions known - Williams is an adviser on the Nottingham Rugby Club's board after playing for the English outfit last year during his recovery from his latest Achilles injury - but Kirwan conceded he had made a big call.
"I think it's an incredibly important time for Ali Williams," Kirwan said.
"He's a 77-test veteran who has been a big part of the Blues. He's had some interesting experiences in the past but he really cares about this place and I believe he's the right man to lead this team. It's a great challenge for him and one I'm sure he'll relish."
Kirwan's hand was forced by Keven Mealamu's decision to take an extended break and forgo the captaincy. Flanker Luke Braid captained the Blues under Pat Lam this year when hooker Mealamu was unavailable, but the strain of the almost weekly defeats began to tell on the 24-year-old.
Apart from Braid, few others within the inexperienced team could be considered captaincy material. The only other contender would have been Tom McCartney, a 27-year-old about to play his sixth season at the Blues.
Williams has had a tough run with injuries during his career and Kirwan will be hoping his Achilles and knee problems aren't an issue, given that his other top-flight lock, Anthony Boric, is returning after neck surgery.
There are still question marks about how Boric will cope physically and mentally from his injury and long layoff.
Kirwan said Williams was ready to prove his doubters wrong.
"He's had a bad run of injuries but I think he's ready for this because he's had a bad run and some people think he's finished. I don't believe that and neither does he."