Edelman declined to comment on the switch, but Golin said the pitch process was non-competitive.
Golin's work with Green & Black's will include launching a series of campaigns, as well as being responsible for the brand's consumer press office.
Golin executive director Claire Culshaw said the agency had been tasked with keeping Green & Black's at the front of consumers' minds, "especially during key calendar occasions or simply whenever consumers are looking for chocolate inspiration".
Golin also handles PR for fellow Mondelez-owned confectionary brand Cadbury. That account includes work on brands such as Creme Egg and Dairy Milk.
A spokeswoman for the agency told PRWeek that because Green & Black's and Cadbury have "very distinct positioning" among consumers, they would be serviced by seperate teams "that will not cross over" on projects.
Green & Black's was established in 1991 and acquired by confectioner Cadbury, which is now owned by Mondelez, in 2005.
Golin's global growth
Golin performed well in 2016, growing five per cent globally and recording revenue of $202m (£156m), according to the PRWeek 2017 Agency Business Report.
In the UK, Golin grew 14 per cent, recording revenue of £25m, up from £22m in 2015, as revealed in the PRWeek UK 2017 Top 150 agency rankings.
Speaking to PRWeek last month, Golin CEO Matt Neale, who manages the agency's EMEA and New York offices, said in 2016 the UK had "a storming year". Golin London grew more than any other office in revenue terms, he said.