Customers who have NFC technology installed in their smartphones are able to tap in and out, TfL's director of customer experience, Shashi Verma said.
"Support for mobile phone payments is live and Contact Assistant will take payments from mobile phones as and when they come onstream."
Contact Assistant is a separate system to the well known Oyster travel card that launched in 2003. With Oyster, billing information is held on each card, but Contact Assistant data is held centrally on a Microsoft SQL Server system, with a new billing engine.
TfL currently process 500,000 joirneys a day through contactless alone, and "usage is growing week by week", Burma added.
The news came as TfL was announced as the fastest growing contactless Visa merchant in Europe for Mastercard and American Express since it began last year.
Scott Abrahams, group head of acceptance and emerging payments at MasterCard UK and Ireland said: "This milestone for TfL shows just how quickly consumers have taken to contactless in London. This extraordinary take up is having a halo effect on other businesses in the UK who accept contactless payments. They are also seeing a significant shift in the way their customers are choosing to pay."
Barclaycard's head of contactless, Tami Hargreaves added: "Having created the technology which sits at the heart of TfL's contactless network, Barclaycard has unique insight into the increasing uptake of contactless among London's commuters.
"Our data shows that the speed, ease and security of paying for travel with a contactless credit or debit card means this is fast becoming a preferred way to pay. We're seeing a steady climb in usage each month and expect this trend to continue throughout 2015 as 'the convenience of 'touch-and-go' becomes the norm."