Mr Walker, 52, was one of the best-known names on The Guardian and was nominated for foreign correspondent of the year in 1997. In 1995 he was considered a candidate for the editor's chair, a post that was won by the paper's current editor, Alan Rusbridger.
Mr Rusbridger said last night: "Martin has had a long and distinguished career on the paper, during which he has reported with distinction from all over the world. We wish him well."
This was followed by an equally terse official statement from the company which said: "Martin Walker has resigned from The Guardian to take early retirement after a career which included postings in Moscow, Washington and Brussels."
Mr Walker issued a statement of his own. "It will be a wrench to leave The Guardian after 28 years, but I have more books to write and new challenges in store," he said.
Ten days ago, Mr Walker was locked in talks with Mr Rusbridger and the paper's managing editor Brian Whittaker about his future career. Immediately, reports began circulating in other newspaper offices about the amount the Brussels operation was costing.
The Guardian's management would not discuss why Mr Walker had made such an apparently rapid decision to depart.Reuse content