And he indicated that he is ready to back moves to remove control of the Brexit process from the Government and return it to the Commons to avoid a "No Deal" scenario .
He accused Nationalists of effectively backing a "No Deal" scenario in Commons votes over their opposition to Prime Minister Theresa May's deal.
Nicola Sturgeon wants Scotland and the UK to remain in the EU customs union and single market and believes Mrs May's deal will be damaging to the Scots economy. The Scottish Government has also published a paper today warning of the damage from a No Deal.
But with just over a month before Brexit day on March 29 Mr Mundell today issued a stark call for the Commons to get behind a deal. It came amid reports the Scottish Secretary has told Mrs May Brexit should be delayed to secure this. "The most important outcome we can achieve is that we get a deal and that we leave in an orderly basis and that we prevent a No Deal Brexit from happening," he said during a speech in Edinburgh.
"But the way to do that is to support a deal. I have been clear about the threat to the Scottish economy and I believe to the continuance of the United Kingdom.
"I have to come to what I think is the obvious conclusion that one of the reasons that Nicola Sturgeon and the SNP are so keen to get this No Deal Brexit is that they realise as well that it is a threat to the continuance of the United Kingdom.
"That's why they're contriving to bring it about by on every opportunity by supporting a No deal Brexit in votes."
Mr Mundell said the SNP's 35 MPs could prove the difference between a deal being struck and rejected. Mrs May's deal has already been rejected overwhelmingly by the Commons over concerns about the Northern Irish backstop. She is now seeking clarifications to this with EU leaders before bringing it back to the Commons.
Mr Mundell was identified today as one of four cabinet ministers who have told the Prime Minister that she has to extend Article 50 or he will back a proposal by Labour MP Yvette Cooper which would allow Parliament take control of the Brexit process.
"I don't comment on private conversations I've had with the Prime Minister," he said.
"What I have said to her repeatedly is that a No deal outcome is a very bad outcome for Scotland and the United Kingdom and that we must do everything that we can to avoid that outcome.
"There's a very, very simple way to avoid that outcome and that is for MPs in all parties to put the interests of Scotland first and vote for a deal - rather than raising the likelihood of a No Deal Brexit."
"I will do everything I can and whatever I deem necessary to avoid a No Deal Brexit coming about - but I'm not making wild suggestions or setting out strict parameters of what they may or may not be."
Nationalist MSP George Adam said: “A number of David Mundell’s colleagues finally realised this week that the Tories’ handling of Brexit has gone from farce to impending disaster. They’ve done the honourable thing and resigned.
“While his own Brexit red lines have been trampled over repeatedly, he doesn’t have the guts to quit. He’s more worried about protecting his own job than protecting the jobs of tens of thousands of Scots.”
“The Tories caused Brexit, they’re forcing this disaster on Scotland against our will and no amount of sophistry from David Mundell will get him off the hook.”