MEC Manchester pitched against Edinburgh-based Feather Brooksbank, the incumbent on the account since 2000, and other agencies, including WPP's MediaCom, to win the business.
The First Group pitch was called in January 2008 as part of a statutory review. The new contract will last four years.
First Group also operates passenger and freight train services, including First Great Western, First ScotRail, First Capital Connect, First TransPennine Express and First GBRf, which were all included in the review.
A spokesman for the company said at the time of calling the review that it was an "opportunity for us to test the market". The review was overseen by Paul Stapleford, who is part of the purchasing group.
The company's roster of creative agencies, including Covey McCormick, Dig For Fire, Guerilla Marketing and LiveFX, were not affected by the process.
First Group runs services in the US under four operating divisions, which were also not affected by the UK review: First Student, First Transit, First Services, and Greyhound.