The agency was chosen by the series maker Initial, part of Big Brother producer Endemol, record company Universal and the BBC, to handle predominantly consumer PR work for the brand.
The agency will work alongside the in-house PR teams of all three firms.
Outside's work on the account is overseen by CEO Alan Edwards, and will seek to attract viewers to the series through PR work across print, broadcast and online media.
The agency will also undertake some trade PR work for the show.
Details of the duration of the account were not disclosed, as the BBC is still closely guarding the broadcast dates of the series to avoid attempts by rival channels to schedule spoiler broadcasts.