Theresa May suffered a second defeat in the House of Commons for her proposed Brexit deal, while new polling indicated another pro-independence majority is expected at Holyrood in the 2021 elections.
Mr Brown said: “This week may come to be seen as the moment that ensured momentum for Scottish independence became unstoppable.
“The events of the last few days have proved beyond question that Westminster isn’t working for Scotland – the complete meltdown over Brexit has shown that clearer than ever.
He added; “You simply can’t trust the UK government to act in Scotland’s interests. The whole Westminster system is broken. It’s time Scotland took our own decisions.”
But Pamela Nash, chief executive of Scotland in Union, said Scots don’t want “any more constitutional chaos.”
“The people of Scotland are fed up with the SNP trying to divide us, they want the threat of an unwanted and unnecessary second independence referendum taken off the table,” she added.