B-M has been selected for the brief having pitched against Chancery Communications, and Equitable's retained agency the Maitland Consultancy.
It is understood that B-M will assume responsibility for a campaign to gain policyholders' backing for plans to secure its long-term future through the £1bn takeover of the firm by Halifax.
Halifax paid an initial £500m for the assurer, with the remaining half to follow if agreement is reached with policyholders on the issue of payouts.
The B-M team is likely to report to Equitable PR head Alistair Dunbar. Maitland will continue as Equitable's retained agency.
As part of the brief B-M will liaise with members of the Equitable Member Action Group, which represents disgruntled policyholders,
The group's chairman Paul Braithwaite told PRWeek earlier this month that Equitable's communications with members had been "a textbook study of how not to handle communications," (PRWeek, 3 August).
The firm's troubles began in July last year when the House of Lords upheld a Court of Appeal ruling that the insurer must honour its commitment to paying bonuses to policy holders.
Unable to meet the £1.5bn fallout from the case, and having failed to find a buyer, the society closed its doors to new business in December.
Controversy erupted again this year when it slashed 16 per cent off the value of its with-profits pensions on the same day that it announced to members Halifax's £1bn takeover.
In December, Equitable chiefs Alan Nash and Chris Headdon resigned amid the crisis, only for it to later emerge that they would pocket £90,000 a year pensions.