Southwark councillors have voted unanimously in support of a motion calling on Transport for London to improve the 42 bus route.
Route 42 links North Dulwich with Shoreditch via Walworth, Bricklayers Arms and Tower Bridge.
Transport for London is expected to launch a consultation next month on plans to introduce double-decker buses on the route to replace the existing fleet of single-deck vehicles.
TfL is also considering extending the route at its southern end to terminate at the Sainsbury's store in Dog Kennel Hill.
On Wednesday night Southwark's Labour, Liberal Democrat and Conservative councillors united to pass a motion condemning the "inadequate" service on route 42 as "unreliable and overcrowded, with people often being left at bus stops".
The motion called on the council's cabinet to lobby TfL for a more frequent and reliable service with double-deck buses.