The appointment comes as GNER settles in to its second ten-year franchise - won in March - to continue to operate the route between London's King Cross and Edinburgh.
Red takes over the account, which spans consumer, crisis and corporate comms, from seven-year incumbent Porter Novelli.
GNER paid the record sum of £1.3bn to keep its franchise, prompting fears among passengers that fares will rise. The amount is around £80m a year more than GNER paid before, it is believed.
Red, which starts work on the brief on 1 September, is charged with boosting passenger numbers during quieter off-peak times.
GNER corporate affairs manager Alan Hyde said: 'There is more of an emphasis on the consumer brief - we need to communicate the advantages of travelling with GNER rather than taking the car or plane.'
Red plans to target travel, lifestyle, food and drink writers and national and regional transport correspondents.
As well as promoting GNER's restaurants, which operate on 100 of its 122 daily trains, Red will push tourist destinations that the lines reach, such as London, York, Durham, Newcastle and Edinburgh, as well as ticket deals on offer.
'We have segmented our market and will be targeting people who want to travel for tourism or leisure, families, students and the grey market, and their respective media,' said Hyde.
GNER also plans a push in the early autumn to plug 30 new 'Mallard' trains, costing £30m overall and currently being built. An ad campaign by VCCP will run alongside a series of 'completion' events and a media relations drive.
Corporate work will include supporting GNER's further bids to run rail franchises in other parts of the country. GNER has teamed up with Hong Kong firm MTR to bid for the network run by the South Eastern Railway in Kent. A decision is expected before Christmas. There are also plans to launch fresh bids, according to Hyde.