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Kirwan made the announcement to the team this morning when they assembled for the first official day of pre-season training for the 2013 campaign.
The second-most experienced player in the 2013 Blues squad with 101 Super Rugby caps, Williams takes the reins from Keven Mealamu who has extended his leave from rugby and relinquished the captaincy to allow someone to lead from the start.
"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."
While Kirwan had taken into account Williams' recent history of injuries, he said the 2-metre lock was ready to take on the responsibility of captaining the side and proving 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.
"I think he's got a heck of a lot to offer this franchise, he's a world class lock with the ability to lead a team and I'm extremely enthusiastic and positive about this decision."
Williams, who returned from England yesterday following the All Blacks' end of year tour, said it was an honour to captain a side he was so passionate about.
"I am a hugely passionate man when it comes to the Blues and it is a great honour to lead the team next year," Williams said. "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."