Sadiq Khan will bring in a one-hour “Hopper” bus ticket which will allow passengers two journeys within a 60-minute window from September.
The first policy of his mayoralty should make it cheaper and more convenient for Londoners to travel around the capital, with those on lower incomes benefiting most.
The Labour Mayor said the ticket, which would cost a single £1.50 fare, would help people who rely on multiple buses to get to work. Many parts of South London, in particular, are heavily reliant on the bus network.
Boris Johnson rejected Lib Dem proposals for a one-hour ticket in 2009 saying it would be too complex and costly.
However, plans for passengers to have unlimited bus transfers within an hour, Mr Khan’s original manifesto promise, are not yet technologically possible for Transport for London.
The transport body’s ticketing technology will be upgraded next year so unlimited journeys within an hour should be a reality by the end of 2018, and perhaps even sooner.
Mr Khan said: “My Dad drove the number 44 bus and transport in London has always been a big part of my life.
“The cost of a fare in London has risen for eight years in a row and now that I’m Mayor I am determined to prevent the cost of travel from becoming a barrier to work.
“The Hopper fare will make life cheaper and easier for millions of Londoners, and will help ensure that everyone will be able to afford to travel around the city.
“This is is just the start of my plan to ensure that travelling around London is affordable for everyone, a commitment that includes a freeze on TfL fares for four years – benefiting millions of people.”
The Hopper fare will automatically be given to all pay-as-you-go passengers with Oyster cards or contactless payments and for most, will mean an end to paying two fares when changing bus.
For the vast majority of passengers this will mean an end to having to pay two bus fares when changing bus.
There were an estimated 2.5 billion bus journeys in the capital in 2015, including 600 million pay-as-you-go journeys. Of these, an estimated 86 million went on to make another bus journey within one hour.
TfL chief Mike Brown, said: “This new option will benefit a huge number of our passengers. For many people catching more than one bus is the only way they can get from A to B.
“This fare will enable us to better meet the needs of those Londoners who live or work in areas which aren’t as well served by Tube or rail services.”
The Lib Dems have been campaigning for a one-hour bus ticket for the best part of a decade.
Their Assembly member Caroline Pidgeon, who stood against Mr Khan for the mayoralty, said: “I welcome our policy being adopted by London’s new Mayor and hope that he will go further and also implement our policy for half price travel for journeys on the transport network before 7.30am”.