Westminster leader Ian Blackford called the plans to replace the controversial border backstop “unacceptable, unworkable, undeliverable and designed to fail”.
Boris Johnson told MPs he had made a "genuine attempt to bridge the chasm" with the EU, and that his proposals were a better option than to "remain a prisoner" of the current deadlock.
But he acknowledged in his statement a day after he shared his proposals with Brussels they are "some way from a resolution".
"This Government's objective has always been to leave with a deal and these constructive and reasonable proposals show our seriousness of purpose," the Prime Minister said.
"They do not deliver everything that we would've wished, they do represent a compromise, but to remain a prisoner of existing positions is to become a cause of deadlock rather than breakthrough.
"So we have made a genuine attempt to bridge the chasm, to reconcile the apparently irreconcilable and to go the extra mile as time runs short."
Jeremy Corbyn responded by saying no Labour MP could support the "reckless deal", which he said would jeopardise the Good Friday Agreement.
They were also criticised by the only Northern Irish MP in the Commons to hear the statement, the independent Unionist Lady Hermon, who claimed Mr Johnson “doesn’t understand Northern Ireland”.
"Boris Johnson's half-baked Brexit proposals are even worse than Theresa May's. They are unacceptable, unworkable, undeliverable and designed to fail - but no one will be fooled by this botched Tory attempt to shift blame for a catastrophic no-deal Brexit.
"The Prime Minister must obey the law and seek an extension - or resign. The SNP stands ready to bring this government down in a vote of no-confidence. We will do everything we can to get rid of Boris Johnson, secure an extension, prevent a no-deal and call an election.”