The former P&O Nedloyd chief executive is leaving to focus on his other commitments, the London listed company revealed in a statement today.
Bob Benton, replaced by Green on 1 August, will return as interim chairman from the next board meeting on 6 March. He previously spent nine years with Clarksons including the last five as chairman.
Since taking the post last year Green has taken on a number of new roles including chairman-designate of Williams & Glyn bank and the same role at construction company Carillion.
“In light of these and other commitments he and the Board recognise that it would be difficult for him to devote sufficient time to Clarksons' growing international shipping services business,” Clarksons said in the statement.
"It has been a privilege to chair Clarksons; it is a world class market-leading business with a very strong management team; however, at this time I recognise the need to focus my responsibilities and therefore, with much regret, I feel it is right to stand down," said Green.
Andi Case, Clarksons' CEO said: "Both personally and on behalf of the Board, I thank Philip for his valuable contribution over the past year and wish him well with his new endeavours."
Green is also standing down as a director of Business in the Community at Clarksons and will formally resign from the board of the company from the AGM on 9 May.
Peter Backhouse, Clarksons' senior independent director, will lead the search process for a new chairman.