The MP for Haltemprice and Howden – one of the safest electoral seats in the UK – stood down from Government last week, days after Theresa May called ministers to desperate crunch talks at Chequers.
Tendering his resignation to the Prime Minister, Mr Davis admitted there had been “a significant number of occasions in the last year or so” when he had disagreed with the Prime Minister’s approach to Brexit.
Mr Davis told BBC’s Newsnight: “I made a decision which was based on a difference of principle.
“I was the Secretary of State responsible for exiting the European Union, the policy being put forward was one that I did not believe in.
“It would have been dishonest to stay and pretend that I did believe in it, and frankly, I would have been useless at it.”
He said the electorate would rather a politician who stood up for their own beliefs, rather than one who tried to support a policy they thought was wrong.
Mr Davis continued: “Do you think the electorate would expect me to do something I thought was wrong?
“That strikes me as entirely implausible.
“My impression of the electorate is that they want you to do the right thing, and the right thing in your own mind.
“They want you to be principled, they want you to stand up for what you believe in.”
Mr Davis said he had several discussions with the Prime Minister about the approach of her Chequers plan, but once it became clear that she wasn’t going to budge, he thought his position was untenable.
He added: “If you’ve got a policy you really have to believe in it, and I really didn’t believe in this, what else did you expect me to do?
“There were lots of discussions that went before and it didn’t change the line.
“It didn’t change the line, I had to go. Simple.”
Mr Davis’ resignation was the first in a long line of Government departures over the Chequers soft Brexit plans, and they came to include former Foreign Secretary Boris Johnson.
So far ten ministers have quit since the meeting ten days ago.