The former Barclays chief executive is thought to be in line to receive up to £30 million following his departure over the Libor rate-fixing scandal.
Mr Diamond, 60, resigned in the early hours of yesterday morning in an about-turn after signalling he had no plans to go.
He was soon followed by another boardroom colleague, chief operating officer Jerry del Missier, on another dramatic day in the City.
One of the most highly paid executives in the City, Mr Diamond is thought to have been paid more than £18m last year.
He is due to be grilled by MPs today over what he knew and when about the rate-fixing scandal, amid allegations that the Bank of England encouraged Barclays to rig the rate it posted at the height of the banking crisis.
Mr Diamond had held on for almost a week after the revelation his bank was to be fined a record £290 million for its part in the Libor interest rate-fixing scandal that has engulfed the institution and the City.
He made his decision after talks with Sir Mervyn King, the Governor of the Bank of England, and Lord Turner, the head of regulator, the Financial Services Authority (FSA).
In another twist, Barclays released a series of documents that appeared to suggest the bank thought it had been given the green light on rate fixing by the Bank of England.
It included a contemporaneous memo from Mr Diamond in which he described a discussion with Paul Tucker, the deputy governor of the Bank of England.
The note was sent from Mr Diamond to Mr del Missier and then chief executive John Varley on October 30, 2008, at a time when Barclays was suspicious that other banks were consistently posting lower rates. In it, Mr Diamond said that Mr Tucker had raised concerns from senior figures in Whitehall that Barclays posted a high Libor rate.
Mr Diamond wrote that he had asked Mr Tucker to explain to Government that Libor quotes from other banks did not represent a true picture.
The American banker said Mr Tucker had told him that the Barclays Libor rate did not "always" need to appear as high as it had.
Barclays said in a statement: "Subsequent to the call, Bob Diamond relayed the contents of the conversation to Jerry del Missier. Bob Diamond did not believe he received an instruction from Paul Tucker or that he gave an instruction to Jerry del Missier.
"However, Jerry del Missier concluded that an instruction had been passed down from the Bank of England not to keep Libors so high and he therefore passed down a direction to that effect to the submitters."
Earlier, there had been a mixed reaction to Mr Diamond's resignation.
LibDem Chief Secretary to the Treasury Danny Alexander told The Herald: "It was absolutely the right thing to do. It was the right thing for Barclays and the right thing for the UK as well.
"It is wholly appropriate that the most senior players take responsibility for one of the most appalling scandals for a particularly scandal-hit period for the banking industry in recent years.
"It does not mean that there are not many other questions that need to be answered by Mr Diamond and others."
Ed Miliband said the move was "necessary and right", adding it was clear Mr Diamond was not the man to lead Barclays through a period of change it needed.
The Labour leader added: "But this is about more than one man – this is about the culture and practices of the entire banking system, which is why we need an independent, open, judge-led public inquiry."
Former LibDem treasury spokesman Lord Oakeshott, who led calls for Mr Diamond to resign, said it was a "great day for democracy". He said Mr Diamond had been the symbol of the "gambling and greed we must root out of our banking system".