John Lewis enlisted MRM last week after a pitch involving The SPA Way and one other agency.
MRM is charged with raising awareness of the brand and its plethora of services, which include home and wedding insurance, tickets for shows and concerts, and travel bookings.
The agency will also help to publicise Source - the Greenbee customer magazine.
Greenbee was launched in a bid to keep pace with changing shopping patterns and the proliferation of online businesses.
MRM founder Richard Wheat heads the account, reporting to Greenbee managing director James Furse.
‘We're looking to build Greenbee from a solid base and take it to the next level,' said Furse.
This month, John Lewis reported a 20 per cent rise in annual profits, driven by a 38 per cent rise in department store profits. It also owns supermarket Waitrose and a third of online supermarket Ocado.