Somerfield announced this week it had received an approach that could lead to a formal bid being made. The news sent Somerfield shares soaring - as PRWeek went to press, they had reached 90p, valuing the company at £435m.
Red Leaf won its IR work following a three-way pitch conducted prior to news of the bid breaking.
The brief marks the first of its kind for Somerfield, which continues to retain incumbent Cubitt Consulting for financial and strategic PR counsel.
It is believed the win is the inaugural client to add to Red Leaf's recently launched IR division, Red Leaf Relations, which is aimed specifically at the private client-broking IR market.
Red Leaf Relations head Susie Staveley joined the agency in mid-February from City firm Broker Profile, where she was a senior consultant, to lead the new division.
'The private client broking market is an important and relevant target audience that is often left untapped. There are corporate brokers who deal with institutions, financial PR consultants who deal with the media and analysts, but there's a gap targeting the private client-broking side,' she added.
Rock music company Sanctuary Records, which has a market cap of £92m, became the second client on Red Leaf Relation's list this month.
That appointment does not affect Sanctuary's relationship with its own City PR incumbent, Merlin Financial.
Red Leaf, headed by CEO Emma Kane, also appointed former Brunswick senior associate partner Katharine Sharkey earlier this year in the newly created role of chief operating officer.
Sharkey joins the consultancy after a six-year stint at Brunswick.