The agency won the account after a competitive pitch against Cheethambell JWT and the previous incumbent, Proximity, following a statutory review.
Ruby, which is in the process of merging with The Red Brick Road, will be responsible for ATOC's 16-25, family and friends, and senior Railcard products. The agency will also work on a new strategic and creative direction for the business.
Activity will span across renewal and CRM activity using outdoor, direct marketing, social media and digital.
Previous advertising for ATOC included a TV campaign, "gnome", to support its train services.
The ad, created by WCRS, followed the path of a pair of gnomes who travel up and down the country on a day out using ATOC's train services.