The prime minister now faces a battle to get the deal through Parliament on Saturday, with the DUP opposing it.
DUP deputy leader Nigel Dodds accused Mr Johnson of being "too eager by far to get a deal at any cost".
European Council President Donald Tusk did not rule out an extension to the Brexit deadline if MPs rejected it.
EU Commission President Jean-Claude Juncker earlier said: "We have a deal so why should we have a prolongation."
But his Brussels colleagues have been more cautious, with Mr Tusk saying he would "consult" the leaders of EU member states about a possible extension if one was requested by the UK.
He said Boris Johnson's acceptance of customs checks at the point of entry into Northern Ireland, which the DUP objects to, had made a deal possible.
Mr Johnson has repeatedly insisted the UK will leave the EU on 31 October and he urged MPs to "come together" and "get this excellent deal over the line".
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