Daily Mail and General Trust is understood to have selected Brunswick within the past week, ending a 12-year relationship with incumbent Tulchan Communications.
The appointment comes after a competitive pitch process first revealed in PRWeek in October 2011.
It is thought the pitch was led by recently installed finance director Stephen Daintith and group comms manager Abi Slater, who moved from Metro in March 2011.
Brunswick declined to confirm the appointment and DMGT could not be reached for comment.
The appointment comes at a delicate time for the media owner as the company faces falling advertising revenues, the declining performance of regional media arm Northcliffe and allegations its titles were among those guilty of phone hacking.
The company is vigorously defending allegations that emerged at the Leveson Inquiry from actor Hugh Grant that The Mail on Sunday had acquired stories via hacking.
The firm responded via PR firm Brown Lloyd James, accusing Grant of ‘mendacious smears’. Late last year, chief executive Martin Morgan said the group was facing ‘considerable’ legal fees to defend the accusations.
In February, the Associated Newspapers owner said that advertising had slid two per cent year on year, to £111m in the three months to 1 January, and that January itself had seen a nine per cent year-on-year advertising fall.
However, overall revenue for the quarter rose two per cent at £495m, boosted by the Daily Mail’s online offering becoming the most visited English language news website in the world.