Barnes, first elected to the London Assembly in 2000, lost his Ealing and Hillingdon seat in May.
As Deputy Mayor Barnes represented the Mayor at public engagements across the capital and internationally.
His work on the Assembly included chairing an inquiry into how the emergency services responded to the 7/7 bombings.
City Hall insiders say Johnson has been looking for a suitable role to reward his former Deputy’s support during his first term as Mayor.
Barnes will be joined on the TfL board by fellow-newcomers Sir John Armitt, Chairman of the Olympic Delivery Authority, Roger Burnley, Managing Director, General Merchandise, Clothing and Logistics for Sainsburys, and Michael Liebreich, Chief Executive of Bloomberg New Energy Finance.
The board is chaired by the Mayor who is supported by Deputy Chair Isabel Dedring.
Mayor Johnson said his new appointments “bring a wealth of experience to the TfL Board” and said they would “oversee delivery of the investment necessary to power London and the UK’s economic development and growth, delivering jobs and access to health, education and leisure across the capital.”
