The political lobbying and media relations specialist is Gumtree's first public affairs agency.
The hire follows that of social media agency 1000heads and PR firm Red Consultancy. Both were appointed in November following seperate pitch processes.
Gumtree head of PR Fergus Campbell, who joined last year and was formerly a director at comms agency Golin, said Red Consultancy and 1000heads' work would be unaffected by the appointment. The three agencies are to work alongside each other.
Initially, PLMR will engage Gumtree's decision makers and stakeholders and build collaboration around the site's work on trust and safety online, the agency said.
"Following this, PLMR will be leading on the public affairs elements of an integrated, public-facing campaign around trust and safety online, which will be launched later this year," a company spokesperson told PRWeek.
Gumtree receives 18.7 million unique visitors in the UK every month. Last year it rebranded for the first time since its inception in 2000. The rebrand included a new logo, brand identity and developments across its mobile and desktop channels.
Click here to read PRWeek's interview with Morten Heuing, UK general manager of Gumtree, who spoke about the "powerful" impact of PR on the business.