
CBS will continue to sell advertising on the transport operator's fleet of 9,000 buses in 40 towns and cities throughout the UK, including Leeds, Manchester, Bristol and London.
Titan had initial discussions with FirstGroup but said it decided not to pitch for the contract.
CBS Outdoor has a long-standing relationship with FirstGroup that stems back to when CBS operated as TDI Group in the '90s.
Jason Cotterrell, commercial director, CBS Outdoor UK, said the FirstGroup partnership "continues to flourish" as both companies work to develop new products.
He said the renewed contract demonstrates the group's confidence in CBS to successfully manage its advertising asset.
CBS Outdoor is trialling a new bus ad format that extends above the roof of single-deck buses, which, it is claimed, makes single-deck bus ads more visible and gives advertisers greater height and stand-out. It is being trialled in York with an ad for the York Museum Trust.
In addition to the bus contract, CBS Outdoor already manages the ads for all FirstGroup's rail franchises, including First Capital Connect, First Great Western, First Scotrail and First TransPennine Express.