Superloop 4, an express Transport for London (TfL) bus service between Canary Wharf and Grove Park in Lewisham, will start running on April 7.
The launch of the new route will take place at the same time as the opening of the Silvertown tunnel.
Buses will run every eight minutes and use the new tunnel as part of their route.
The service will be the last of 10 Superloop routes to be rolled out, and will also call at stops in Lee, Blackheath and Greenwich.
An existing Lewisham bus route will also be extended north of the river once the tunnel opens.
Route 129 will no longer end at the O2 in Greenwich, but instead continue on to Great Eastern Quay in Newham.
New stops include Silvertown, London City Airport and Beckton, with buses on the route running every eight minutes.
Route 108 will continue to operate every ten minutes between Lewisham and Stratford via the Blackwall tunnel.
TfL has said that these three routes will allow 21 buses to cross the river every hour, more than tripling the current capacity.
A new bike shuttle service will also start running to transport cyclists through the 1.4km tunnel.
The service will operate every 12 minutes, seven days a week from 06.30am to 9.30pm.
It will have two stops, one north if the river in Seagull Lane close to Royal Victoria DLR station, and one south of the river in Millennium Way near the junction with Old School Close.
Stagecoach London Managing Director Paul Lynch said: “We’re excited to be asked to operate the innovative and important Silvertown Tunnel cycle-shuttle service as part of the enhanced cross river public transport offering.
“We’re busy making sure our specially converted zero emission buses will be ready in time. We also hope to see the new tunnel ease traffic conditions for our other bus services in the area.”
All three of the cross-river bus routes will be free for at least a year, as well as cross-river journeys on the DLR, from Cutty Sark to Island Gardens, and from Woolwich Arsenal to King George V.
