The agency has been taken on for a six-figure sum after fending off rivals Clarion and Bell Pottinger.
The supermarket chain has reported a growing market share for the second successive quarter while Tesco's share has dipped, according to figures by TNS Worldpanel.
Morrisons has enjoyed a change in fortunes since undergoing a £450m brand makeover last year. In 2005 it came bottom in PRWeek's Reputation Monitor of press coverage for 2005 (PRWeek, 9 December 2005).
Citigate Dewe Rogerson is retained for financial PR. Morrisons would not reveal whether there was an incumbent for corporate and consumer.
