"Sir Robert is 60 in August and told the board some time ago that he wanted to retire this year," a spokesman said.
Railtrack said the timing of the announcement was not related to the rail summit earlier this week, in which railway standards were criticised by the Government.
Sir Robert has been chairman of Railtrack since its formation in 1994 and helped steer the privatised track operator to its pounds 2bn flotation two years later.
His departure brings to an end another chapter in a career studded with controversy. His reputation reached its nadir during the latter stages of his 30 year career at BP. By the time he became chairman of the oil giant in 1990 BP was a bloated under-achiever.
Cuts were inevitable but he did nothing to endear himself to workers with his abrasive style. It was during an interview with Fortune magazine that he made a remark that came to haunt him: "Because I am blessed by my good brain, I tend to get the right answer rather quicker and more often than most people."
He became one of Britain's most unpopular industrialists and in 1992 was ousted in a boardroom coup. "I don't think I'm arrogant and abrasive," he said later. "I tend to say what I think and don't disguise it."
His popularity was further dented when he moved to Railtrack and within months the network ground to a halt due to a bruising industrial relations dispute.
He tried an oil industry comeback with JKX Oil and Gas, though that too ended in failure. The company was rescued in 1997 by a pounds 55m takeover from Ramco Energy at a fraction of the issue price.
Railtrack shares closed 77p higher yesterday at 1552p.