The remit will include traditional and new media, with input from MRM’s social & digital and public affairs teams.
The account was previously held by KL Communications.
Redington is the UK’s fourth-largest investment consultancy, with £368bn of assets under advice.
MRM will report to head of marketing Dave McGovern, who said: "We have set ourselves a hugely ambitious target of making 100 million people financially secure. Throughout the selection process MRM showed us they really bought into our vision, showing clear passion and determination to help us engage with a much wider audience."
MRM director and co-founder Andrew Appleyard called Redington "a hugely dynamic and exciting business at the vanguard of innovation within the UK pensions space".