Trump met with Xi at a summit last June when he "stunningly turned the conversation to the US presidential election, alluding to China's economic capability to affect the ongoing campaigns, pleading with Xi to ensure he'd win," Bolton says.
The allegation that Trump asked the leader of a major US adversary to help him win the next election will reverberate across Washington six months after Trump was impeached on charges he sought help from Ukraine with his reelection bid.
The United States on Tuesday sued Bolton, seeking to block him from publishing a book about his time in the White House that it said contained classified information and would compromise national security.
The civil lawsuit came one day after US President Donald Trump said Bolton would be breaking the law if the book were published.
The book, entitled The Room Where It Happened, is due to be released on 23 June.
Bolton also addresses the claims that formed a central part of the president's impeachment trial.
In January, President Trump was impeached for withholding military aid to pressure Ukrainian President Volodymyr Zelensky into starting a corruption investigation into Democratic presidential hopeful Joe Biden and his son Hunter.
The president denied the reports and Trump was acquitted after a two-week trial in the Republican-controlled Senate, which did not include any witnesses.
Bolton says the inquiry might have had a different outcome if it had gone beyond Ukraine and investigated other instances of political interference.
He had joined the White House in April 2018 and left in September the following year, saying he had decided to quit as national security adviser. President Trump, however, said he had fired Bolton because he disagreed "strongly" with him.