The account is focused on the social networking company’s advertising services, which are predicted to bring in revenues of £300m this year.
Nelson Bostock CEO Lee Nugent said his agency had not been asked to repitch for the account, but "it was the right time for the agency and the client to move on".
Edelman takes over the account today and will report to Facebook UK & Ireland head of PR and communications Sophy Tobias.
Tobias declined to comment on whether Facebook had offered other agencies the chance to pitch for the account.
The remainder of Facebook’s UK PR activity will continue to be handled by Blue Rubicon.