From today, passengers will only be able to pay for bus fares using an Oyster card, contactless credit or debit card or travelcard ticket.
TfL estimates less than one per cent of journeys are currently paid for with cash, down from 20 per cent in 2003.
TfL director of buses Mike Watson said: “The way our customers pay for goods and services is evolving, so we need to ensure our ticketing evolves too.
“Removing cash from our bus network not only offers customers a quicker and more efficient bus service but it enables us to make savings of £24m a year which will be re-invested to further improve London's transport network.'
A new “one more bus journey” feature has also been added to Oyster cards so that anyone without enough credit is able to make the journey and top up later.