Boris Johnson will warn derailing Brexit would be a "disastrous mistake" as he claims some Remain supporters are more determined than ever to stop Britain quitting the European Union.
The Foreign Secretary will insist leaving the bloc is a cause for hope, not fear, as he gives a speech in central London setting out aims for uniting the country as exit day grows closer.
Johnson is also expected to warn that having to adhere to EU directives would be "intolerable" and "undemocratic."
He will say Remainers should not be told to "get over it" because many have "noble sentiments." To make Brexit a success, supporters must "reach out to those who still have anxieties," he will urge.
Johnson will say: "I fear that some people are becoming ever more determined to stop Brexit, to reverse the referendum vote of June 23 2016, and to frustrate the will of the people.
"I believe that would be a disastrous mistake that would lead to permanent and ineradicable feelings of betrayal. We cannot and will not let it happen.
"But if we are to carry this project through to national success - as we must - then we must also reach out to those who still have anxieties.
"I want to try today to anatomise at least some of those fears and to show to the best of my ability that they are unfounded, and that the very opposite is usually true: that Brexit is not grounds for fear, but hope."
But opponents have pointed to his campaigning methods during the referendum. Labour's Chuka Umunna, who supports the Open Britain campaign against a hard Brexit, accused Mr Johnson of hypocrisy.
He said: "Boris Johnson is totally unqualified to preach about the perils of fear and betrayal when he engaged in disgraceful scaremongering with his ridiculous assertion that Turkey was on the verge of joining the EU and he has already betrayed millions of people by going back on his pledge to secure £350 million extra per week for the NHS.
"This is hypocrisy of the highest order."
Johnson's speech is the first of six being made by Prime Minister Theresa May and senior Cabinet figures to set out the Government's road map for Brexit.
Brexit Secretary David Davis, International Trade Secretary Liam Fox and Mrs May's deputy David Lidington are expected to speak in the coming weeks.