The former Labour prime minister said MPs dismissing concerns about the future of the boundary between Northern Ireland and the Republic were “sickening”.
He also said Theresa May’s demands for Brexit were “literally not going to happen” in a dramatic intervention ahead of the PM’s next showpiece Brexit speech on Friday.
Speaking on BBC Radio 4’s Today show, Mr Blair said: “What she thinks is that it’s possible to get the EU to give us access to Europe’s markets without the same obligations that the rest of Europe has in the single market.
“That is not possible. It’s not a question of a tough negotiation or a weak negotiation, it literally is not going to happen.
He added: “I find it not just disappointing but sickening that people should really be prepared to sacrifice peace in Northern Ireland on the altar of Brexit.”
And Mr Blair cautioned that despite Jeremy Corbyn’s call for Britain to stay in a customs union with the EU after Brexit, Labour would “very soon find that we’ve got to move further in order to escape the dilemma ourselves”.
He will give his own speech on Thursday, following on the heels of John Major, the Conservative prime minister he ousted in 1997.
Mr Blair will aim his address at Brussels, telling EU leaders that they “share the responsibility to lead us out of the Brexit cul-de-sac”.
He is expected to call for them to set up a “parallel path” to Brexit, which gives Britons the option to stay in a “reformed” EU.
There may be just “weeks” left to do so, Mr Blair will declare, buoying Remainers with the optimism that “in these times in politics anything can happen”.
It will come hours after Theresa May hosts EU Council President Donald Tusk in Downing Street for talks on the draft Withdrawal Agreement.
On Wednesday, she said the terms laid down by Brussels could not be accepted by “any UK prime minister”.
Mr Tusk has already hit back in a speech to business leaders, saying he will ask Mrs May for a better solution to prevent a hard border in Northern Ireland than it staying in a “common regulatory area”.
“No-one has come up with anything wiser,” he claimed.