Sadiq Khan refused to answer questions on whether there was a private pay-off between his office and former Metropolitan Police commissioner Dame Cressida Dick.
It comes after lawyers said that, without one, she could have grounds for a harassment claim against him.
The London mayor was speaking in public for the first time since issuing a statement criticising a report by Sir Tom Winsor that said Dame Cressida “felt intimidated” into quitting earlier this year.
Asked directly about the issue of a pay-off, Mr Khan responded: “We saw over the last year and more, trust and confidence from Londoners in the Met Police Service and the commissioner plummet to record low levels.
“I’m afraid the former commissioner failed to come up with a plan to respond to that crisis and the plan to win back the trust and confidence.
“I don’t apologise at all for standing up for Londoners.”
Asked again whether there was any form of private settlement, Mr Khan said: “I’m quite clear that I don’t accept the findings of this biased report from Winsor, who failed to look at all the facts.
“And what Londoners want to see is a mayor doing his job he’s required to do by statute – holding the commissioner to account – and if the Prime Minister, the Home Secretary, the policing minister, and Tom Winsor don’t agree, that’s their problem, not mine.”
The former chief inspector of constabulary had been ordered by then-Home Secretary Priti Patel to conduct a review into the circumstances surrounding Dame Cressida’s resignation.
She quit in February after Mr Khan made it clear he had no confidence in her plans to reform the force, ultimately leaving in April.
Two months later, the Met was put into special measures by the Her Majesty’s Inspectorate of Constabulary and Fire and Rescue Services.
Sir Mark Rowley is due to take over as commissioner this month.