The company was formed as an 'arms-length' successor of the South Yorkshire Passenger Transport Executive (SYPTE) in 1986, which was broken up as a result of the deregulation of bus services.

South Yorkshire Transport operated buses in and around Doncaster, Rotherham and Sheffield with some services extending to Chesterfield, Leeds and Barnsley.

[1] A 20% stake in the company was divested to FirstBus from the Stagecoach Group in 1995, and eventually in 1998, First purchased Mainline, later rebranding the operation to First South Yorkshire.

[2][3]: 132 In the months prior to deregulation, fare increases of up to 300% were enacted and staff redundancies across the company were carried out in order to cover running costs commercially.

[5][1] Throughout the late-1980s and early-1990s, South Yorkshire Transport faced serious competition from a number of independent operators and group subsidiaries in and around Sheffield.

[10][11] South Yorkshire's acquisitions, creating an operating area of 1.65% of the United Kingdom, had previously attracted the attention of the Office of Fair Trading and the Monopolies and Mergers Commission, with the company being referred to the House of Lords and the mergers of both SUT and Sheaf Line being ruled as against the public interest at the time.

Sheffield Omnibus, meanwhile, would compete independently until 1995, managing to purchase fleets of Alexander PS types on Volvo chassis and Alexander-bodied Leyland Olympians on lease before it was merged into the Traction Group with Andrews.

[citation needed] Buses in Rotherham were based at a large garage on Midland Road, which was also home to the central engineering works of South Yorkshire Transport.

[22] Following the sale of the company to FirstBus, the Midland Road works were retained and later repurposed as the FirstGroup's Commercial Unit for the repainting and refurbishment of the group's buses.

[27] However, Mainline soon decided not to commence services and pulled out of Ipswich, selling their operations and the ten Volvo B6s to Eastern Counties.

[20] Prior to the acquisition of Mainline by FirstBus, the company had amassed a total of 180 Volvo B10M single-deck buses with Alexander PS type bodywork from 1990 to 1996.