Ian Blackford has said SNP MPs have prepared a vote of no confidence in the Prime Minister and has called on other opposition parties to back a move to oust Boris Johnson.
He challenged Labour leader Jeremy Corbyn and Lib Dem leader Jo Swinson to "step out of the sandpit and step up to the job", in his bid to evict the "dangerous Tory government" from Downing Street.
He branded Mr Johnson's Conservative administration at Westminster as "dysfunctional", while accused the PM of trying to be "his own Etonian version of Donald Trump".
Mr Blackford said if the Queen's Speech, due to be delivered on Monday, "ever comes to a vote, then the SNP will vote it down".
But he also said the SNP had prepared a vote of no confidence in the Prime Minister.
He added while his party had "worked well" with opposition parties to try to halt Brexit, he warned Labour and the Liberal Democrats that their patience "has limits".
Mr Blackford, speaking at the start of the SNP annual conference in Aberdeen, insisted: "We should not be tolerating this Tory government in office at all.
"We must force this dangerous Tory government out of office and let me tell you, the SNP is primed and ready to do just that. The SNP has prepared a vote of no confidence."
He challenged Labour and the Liberal Democrats to back this, saying: "Let's come together, let's back a vote of no confidence, let's get rid of Boris Johnson."
He told Mr Corbyn and Ms Swinson: "Jeremy, Jo. The clock is ticking.
"The SNP is ready to act. Are you?"
Mr Blackford continued: "My clear message to Labour and the Liberal Democrats is this - the SNP is not in the business of propping up a Tory government, nor should you be."
Labour has rejected calls for action which could tee up a general election until it is confident the possibility of a no deal Brexit is ruled out.
