The former home secretary has said he was approached by the Labour leader earlier this year but turned down the offer of a new frontline role.
“Ed said to me a few months ago ‘I suppose you’re not interested in coming back?’ I said ‘No’,” he said in an interview with Alastair Campbell for GQ magazine.
Mr Johnson has previously ruled himself out as a contender for the Labour leadership, despite pressure from MPs who believe they would stand a much better chance in next year’s general election if he replaced Mr Miliband.
He insisted the party could win in May, despite Mr Miliband’s dismal poll-ratings, and said he had told the Labour leader he would be happy “to go round the country, campaigning, talking to parties” during the election.
He indicated, however, that he could even be tempted back to the frontbench if Labour succeeded in regaining power.
“Disgracefully - and it is disgraceful because I won’t have done the heavy lifting - then I would be more interested. But I am not gagging for it,” he said.
Since standing down as shadow chancellor in 2011 after discovering his wife was having an affair with his police protection officer, Mr Johnson has carved out a successful second career as a writer, penning two best-selling volumes of his autobiography.