Mr Bercow was accused by some Brexit-backing MPs of siding with Remainers during his time as Speaker.
"I think that Brexit is the biggest foreign policy mistake in the post-war period, and that is my honest view".
Addressing a gathering of the Foreign Press Association in London yesterday, Mr Bercow said while he was impartial in chairing proceedings in the chamber, he could now express an opinion.
He added: "I don't think it helps the UK".
John Bercow served as the House of Commons Speaker for 10 years before stepping down late last month.
However, he added: "My own personal opinion is that Brexit does not help us".
Addressing the divisive and at times bad-tempered debates over the UK's attempts to exit the European Union - with the final steps slated for right after the 12 December vote, Bercow argued the Parliament is no disgrace at all and "did its job well" in a jab at Attorney General Geoffrey Cox's remarks about the "zombie Parliament".
Ex-Labour MP Kate Hoey alleged that he had been a "Remain Speaker" in an interview with talkRADIO, and Sir Bernard Jenkin said he had been guilty of "pleasing one lot and not the other" in Commons debates on Brexit.
The 62-year-old former deputy speaker was elected after securing more than half of votes in the fourth round of voting by MPs on Monday.
Sir Lindsay said he wants to ensure that backbenchers are still able to hold ministers to account while enabling parliamentary business to be conducted in "the best possible way". "The honest answer is no, I don't", he said.
Mr Bercow left the role after a decade which has been viewed as a time of reform but also controversy.