In a resignation letter posted to Twitter on Thursday morning, Raab said he could not support a deal, with specific reference to its provisions on Northern Ireland, that presented “a very real threat to the integrity of the United Kingdom”.
He added he could not support an “indefinite backstop arrangement” that he said would see the EU hold veto of the UK’s ability to fully quit the union.
“The terms of the backstop amount to a hybrid of the EU customs union and single market obligations,” said Raab.
“No democratic nation has ever signed up to be bound by such an extensive regime, imposed externally without any democratic control over the laws to be applied, nor the ability to decide to exit the arrangement.
“That arrangement is now also taken as the starting point for negotiating the future economic partnership. If we accept that, it will severely prejudice the second phase of negotiations against the UK.”
Raab added the deal also defied manifesto promises made by the Conservative party at the last election.
The cabinet held a five-hour meeting on Wednesday and eventually backed Theresa May’s Brexit plan.
Northern Ireland minister Shailesh Vara also announced his resignation on Thursday, stating the deal left the UK at a “halfway house” with no certainty on when it would become a sovereign nation.