Blair, a leading voice against the UK's decision to quit the bloc, said Britain could be persuaded to stay if concerns about migration and other issues were met, urging European leaders to take the initiative to "lead us out of the Brexit cul-de-sac".
It is the second major Brexit intervention by a former prime minister in as many days after John Major said Britons should be given another chance to vote, arguing they were misled about the consequences of their June 2016 referendum.
"Europe knows it needs reform. Reform in Europe is key to getting Britain to change its mind," Blair said in a speech in Brussels.
Blair, prime minister from 1997 to 2007, said a "comprehensive plan on immigration control" would help sway opinion on Brexit and could also turn the tide of populism and dissatisfaction seen across Europe in recent years.
"If... Europe was to offer a parallel path to Brexit of Britain staying in a reforming Europe, that would throw open the debate to transformation," he said.
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