The agency beat off competition from Ogilvy and WCRS following a seven-month process.
The Post Office has recently been working with FCB Inferno, which will retain its digital and direct business despite being kicked out of the ad review. Post Office originally called an ad, digital and direct pitch but then narrowed it to just advertising.
Campaign broke the news on the review in April, and an initial discovery meeting took place in May.
The Post Office confirmed the appointment and said it could not comment further.
The incumbent is Dare, which was unable to re-pitch for the account because it was not selected for the Government’s creative agencies roster. When Dare won the business in 2009 the account estimated to worth £12 million.
Earlier this month the Post Office launched its first Christmas campaign on TV in five years. The campaign, created by FCB Inferno, included a 60-second spot featuring the actor Robert Webb and the singer Pixie Lott.
FCB Inferno and its predecessors have worked with the Post Office on its CRM since 2004.