Morrisons is the last of the 'big four' supermarkets to launch its own clothing range, and Nutmeg will compete with Asda's George, Tesco's F&F and Sainsburys' Tu.
It will be in stores at the end of March and will debut with an offer for children aged 0-12 and an 'essentials' range for all ages.
Following a three-way pitch, Cake's team will develop and implement a consumer PR launch strategy as well as managing ongoing press office activity for the launch.
Michele Charles, head of PR and social media at Cake, will lead the account, reporting to Eileen McGuinness, head of consumer media and brand campaigns at Morrisons. McGuinness said the agency would take 'a fun, family-focused approach'.
It is the first time Cake has worked for Morrisons, which used Focus PR to help launch an online wine offering in September.
Supermarket clothing sales grew 6.2 per cent in the year to November 2012, according to research from Kantar Worldpanel in January.