Nieri will join PAA in the autumn to replace the founder, Phil Andrews. The appointment will allow Andrews to concentrate full-time on his role as the chief operating officer for Engine Group in the UK, a position he took on in January last year.
Nieri joined CMW from Rapp more than ten years ago and was promoted to managing director in 2006 following the departure of the agency's founder, Janet McKay.
Since then he has overseen a repositioning of the agency, hiring the creative directors Jamie Bell and Iain Hunter and guiding it to second place in Campaign's Direct Agency of the Year award category for the past two years.
At PAA, Nieri will lead the agency's 100-strong team, helping to develop client relationships and boost its new-business presence.
He will work closely with Andrews, who retains the role of founding partner, to help provide strategic advice to key clients, and Steve Aldridge, the chairman and creative partner.
Andrews said: "Handing over the reins of the agency that I founded with Steve 13 years ago was never going to be easy, but in Martin we have found an exceptional leader who I am confident will take PAA into its next stage of development."