Gordon, who leaves Number 10 this month, will be going into business with Labour regional press officer for the West Midlands Caroline Badley.
It is understood that Gordon and Badley will be assisting MPs and others with their communications. Gordon told PRWeek she would be providing comms support to a 'diverse client base'.
Gordon is highly rated by Labour insiders and seen as a party loyalist. Her departure is a blow to Labour supporters concerned about Brown's plummeting poll ratings.
One Labour source said: 'The party needs people like Fiona right now, right at the centre, helping us all get through this very difficult period.'
Gordon's partner is Steve McCabe, the Labour whip who co-ordinated the botched Crewe by-election campaign.