Mr Kwarteng, who was sacked by Ms Truss after introducing her tax-cutting agenda said there was "no tactical subtlety whatsoever".
He told The Financial Times: "People got carried away, myself included. There was no tactical subtlety whatsoever.
"My biggest regret is we weren't tactically astute and we were too impatient. There was a brief moment and the people in charge, myself included, blew it."
Mr Kwarteng has spoken publicly only a handful of times about his disastrous mini-budget and ousting from government, as Prime Minister Rishi Sunak and Chancellor Jeremy Hunt promptly shifted direction in a bid to reassure financial markets.
Ms Truss was ousted after seven weeks in power, when her tax cuts spooked the markets.
The MP for Spelthorne in November previously claimed he told Ms Truss to "slow down" her radical economic reforms or risk being out of No 10 within "two months".
His latest intervention came after Mr Hunt unveiled so-called his "Edinburgh reforms" ― 30 changes expected to turbocharge growth, including by easing capital requirements for smaller lenders.
Mr Kwarteng had hoped as chancellor to oversee a "Big Bang 2.0" ― a reference to Margaret Thatcher's 1986 policies that kicked sweeping changes in the City of London.
The now-backbench MP criticised Ms Truss's "mad" decision to sack him as chancellor for implementing her plans, while refusing to apologise for the financial turmoil unleashed by their disastrous mini-budget.
Kwasi Kwarteng sacked as UK Chancellor — in pictures
Using more than £70 billion of increased borrowing, he set out a package which included abolishing the top rate of income tax for the highest earners and axing the cap on bankers' bonuses, on top of a massively expensive energy support package.
The mini-budget triggered turbulence in the financial markets, sending the pound tumbling, forcing the Bank of England's intervention and pushing up mortgage rates.
Two days later, he signalled more tax cuts were on the way, spooking markets further.
Mr Kwarteng's latest comments came after Ms Truss's former chief speech writer said she took a "Spinal Tap approach" to government, demanding the volume was "turned up to 11".
Asa Bennett said the former prime minister had arrived in Downing Street determined to put "rocket boosters" under the economy and that it was a matter of "bitter regret" that her efforts had failed.
Ms Truss's short-lived premiership ended in humiliation after her mini-budget led to chaos on financial markets forcing the Bank of England to take emergency action to prevent pension funds collapsing.
Ms Truss resigned after only 44 days in office, with her economic measures swiftly ripped up by Chancellor Hunt and her successor at No 10, Mr Sunak.