In remarks to the House of Commons, Johnson criticized Prime Minister Theresa May's plans for exiting the EU, describing it as a clean departure "in name only." Britons should be "great independent actors" on the world stage, not "rule takers," he said.
"It is not too late to save Brexit," Johnson said. "We have time in these negotiations. We have changed tack once and we can change again." May's government published a white paper last week with long-awaited proposals for Britain's relations with the EU after it leaves the bloc next year. The document proposes keeping Britain and the EU in a free market for goods, with a more distant relationship for services.
The plan has infuriated fervent Brexit supporters, who think sticking close to the bloc would limit Britain's ability to strike new trade deals around the world. Johnson and Brexit Secretary David Davis both quit the government in protest and May has been struggling to quell rebellions within her own ranks ever since.
Lawmakers earlier confronted May during her weekly question-and-answer session in the House of Commons. With May's support faltering, members of her own party, including Davis, felt emboldened to ask critical questions about her way forward.
Brexit supporter Andrea Jenkyns launched the first salvo in an open challenge to her leader, suggesting policies unveiled last week were closer to those who want to remain in the EU than to those who want to leave.
"Can the prime minister inform the House at what point it was decided that Brexit means Remain?" Jenkyns asked. Shouts rang out across the Commons. "At absolutely no point because Brexit continues to mean Brexit," May replied.
Even Davis jumped into the bad-tempered exchanges, asking May to publish the legal draft of a free trade treaty. Davis' former deputy, Steve Baker, chimed in to ask about contingency plans for a no-deal departure.
The session offered a mirror on a party deeply split and a government just scraping by to stay in power. Though Johnson did not call for May's ouster, his remarks before the pre-recess session, will at the very least remind hardliners of the initial vision behind the referendum. Johnson suggested it was a vision May herself had shared before the "fog of self-doubt had descended."
Johnson told lawmakers that the government had "dithered" and failed to make the case for a free trade agreement outlined in the January 2017 speech at Lancaster House in the heady months after the referendum passed. It was not the plan agreed by the government earlier this month at May's country retreat at Chequers, he said.
"Let us again aim explicitly for that glorious vision of Lancaster House — a strong, independent self-governing Britain that is genuinely open to the world, not the miserable permanent limbo of Chequers," he said. "Not the democratic disaster of ongoing harmonization with no way out and no say for the UK. We need to take one decision now before all others and that is to believe in this country and what it can do."
Johnson insisted there was still time to adjust and that the country must do so because much was at stake. "We must try now because we will not get another chance to do it right," he said. May also sought to rally support in later meetings with Conservative Party backbenchers known as the 1922 Committee and with the Parliamentary Liaison Committee that includes the leaders of all the House of Commons select committees.
She received at least a measure of support from the 1922 Committee, including the announcement by one lawmaker that he had withdrawn a letter calling for a confidence vote that could threaten May's position as party leader.
Even such a small change could be important — if 48 legislators submit letters seeking a confidence vote on May's stewardship of the party, it automatically triggers a leadership vote. Parliament plans to begin its long summer recess Tuesday after a feverish series of debates on Brexit policy.
Gregory Katz in London contributed.