Since the Overground was created in 2007, investment in new trains, refurbished stations and visible staffing has seen the service achieve high levels of passenger satisfaction.
In addition, the latest Network Rail figures rank it as the second most reliable surface railway in the UK.
The new link connects Wandsworth Road, Clapham High Street, Denmark Hill, Peckham Rye, Queens Road Peckham and Surrey Quays to the service and offers commuters in South East London a range of new connections.
Mayor Johnson said it would “help serve those rapidly regenerating parts of East London where the job market is expanding and will support further growth.”
The Mayor, who is lobbying Ministers for greater control of the capital’s rail network, added that the new route was “a real blueprint for rail services of the future and a brilliant addition to our transport network.”
Transport for London says a journey between Clapham Junction and Surrey Quays will take 24 minutes, while a trip to Canada Water and its interchange with the Jubilee line will take 28 minutes.
In addition, the link enables passengers to reach a number of popular destinations without first travelling into Central London.
Transport Secretary Patrick McLoughlin said: “London is the economic powerhouse of the UK and we know how important it is to invest in the capital’s transport network – that is why we have contributed nearly £60m towards this transformational project.
“This final connection across South London will be a boon for businesses and commuters alike and I congratulate all those who worked on this successful scheme.”
Mr McLoughlin declined to comment on the likelihood of the Mayor and TfL succeeding in their efforts to gain control of further surface rail services but praised Mr Johnson as “a great lobbyer” for London.
Commenting on the Overground’s success, Mr Hendy said the service “really has been a case of ‘if you build it, they will come’.”
He added: “Since TfL took over management of the line five years ago, Londoners from all parts of the capital have been flocking to it to take advantage of its spacious, air-conditioned trains, its fast and frequent timetable and its safe, clean, upgraded and passenger-friendly stations.”