The Woolwich Foot Tunnel has reopened after work to bring the structure up to date.
New lifts, stairs, lighting and CCTV have been installed in the Victorian structure, while the tunnel itself has been refurbished.
It follows the recent refurbishment of the nearby Greenwich Foot Tunnel, also in south-east London.
Greenwich Council thanked cyclists and pedestrians for their patience while works were ongoing.
Between them the tunnels are used for 1.5m journeys a year. The joint refurbishment cost £11.5m.
"It's great news that the Woolwich Foot Tunnel will be open - particularly in time for Christmas when public transport options are much more limited," Councillor Denise Hyland, cabinet member for regeneration.
"It's a free and easy means of crossing the river."
She said it was an "extremely complex heritage project".
"It is the first time since the tunnels were built that work of this extent has taken place and it's not been without its challenges," she said.
"I thank pedestrians and cyclists for their ongoing patience while we have carried out these complicated works."
At the moment the lifts are not working, so Greenwich Foot Tunnel will not have disabled access until the new year.