Stothard's departure had been expected, as he had indicated in the past that he would leave this year when the newspaper was at a high point in its history.
He announced his decision at 6.30pm yesterday, following a day's speculation about his future at Times publisher News International -- owned by News Corporation -- and about the title.
In last night's short speech to staff, Stothard described editing the newspaper as "the greatest job in journalism". He took the post in September 1992, after serving as deputy editor for six years and as the newspaper's Washington correspondent.
In a statement, News Corp chairman Rupert Murdoch said: "Professionally, Peter's editorship will be remembered as a great era in the newspaper's long history. Personally, I will always value Peter as a colleague of great intellectual talent."
During Stothard's editorship the newspaper's circulation has grown from 377,000 to 711,000. Stothard has led journalistic campaigns including a battle with the former Tory treasurer Lord Ashcroft and a campaign against Greg Dyke's appointment as director general of the BBC.
Stothard was absent from the newspaper for nine months during his editorship during 2000 while he underwent chemotherapy to treat a tumour of the pancreas. This time he is said to be leaving to pursue other interests.
The appointment of a new editor will be closely watched by Downing Street, as Tony Blair is said to believe the newspaper is the most influential in the UK among undecided voters.
His potential replacement Thomson is said to have become a close associate of Murdoch in recent months and he is believed to have convinced the Australian-born media tycoon that changes are needed at the paper.
If Thomson, also an Australian, is appointed he will become the first non-Briton to hold the post.
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