Route 312 commenced on 1 September 1990, replacing witdrawn route 12A. Route 312 originally ran between Peckham Garage and South Croydon Swan & Sugar Loaf. The route initially operated from Thornton Heath (TH) using Leyland Olympians.
On 12 March 1994, the allocation was moved to Croydon (TC) garage.
On 17 March 2001, the route was converted to low floor using Alexander ALX400 bodied DAF DB250LFs.
On 3 September 2005, the route was withdrawn between Norwood Junction and Peckham - this section replaced by route 197 and route 312 was converted to single deck operation using Plaxton Pointer 2 bodied Dennis Dart SLFs.
On 4 September 2010, the route was retained by Arriva London.
On 5 September 2015, route 312 was retained by Arriva London with new and existing Optare Electric MetroCitys.
Route 312 operates via these primary locations:
- South Croydon Bus Garage
- Croydon High Street
- East Croydon
- Norwood Junction