Bryn Hall will remain the Blues' No 1 halfback after his strong season this year, but the addition of Cowan strengthens the position considerably.
"Jimmy brings competitiveness, plenty of experience and great game awareness, which is something we were really looking for," Kirwan said.
"We've got some good young guys coming through in Bryn Hall, Ihaia West and Simon Hickey coupled with Dan Bowden coming back but we still felt we were lacking a bit of experience through that combination.
"Piri Weepu left a bit of a hole but we think Jimmy's really going to step into that role and be fundamental to the growth of this franchise."
Former Southland and Highlanders player Cowan, 32, who now represents Tasman in the ITM Cup, said he was looking forward to returning to Super Rugby following a two-year stint with Gloucester.
"I'm excited about moving up to Auckland to join the Blues and feel I can really contribute towards helping them achieve success."
Kirwan said he still had five or six spots to fill for next season's roster and was continuing to watch the ITM Cup with interest.
