The agency scooped the brief, which will see it promote St Pancras as the "destination station", after a pitch against Gyro International, 23Red and Meteorite.
Hurrell Moseley Dawson & Grimmer previously handled advertising for the station and relaunched St Pancras, following the completion of the construction of the Channel Tunnel Rail Link, in January 2007.
Walker Media won the media planning and buying account at the same time.
Ruby will now work alongside the London Communications Agency, which handles St Pancras' media relations and PR.
Maureen Bannerman, the retail and marketing director at St Pancras International, said: "High-speed domestic train services are set to bring new visitors to the station and with our strong communications team in place, we can continue to maximise the potential of this amazing place."
This article was first published on campaignlive.co.uk