His exit comes five months after he lost the Quebec Liberal leadership race to Philippe Couillard, finishing a disappointing third.
Bachand had been minister of economic development, then finance, through five turbulent years during which he implemented a stimulus program and drew the wrath of student protesters with tuition hikes.
Before his career as an elected politician, Bachand was a corporate executive, a lawyer, a founding member of Oxfam Quebec, and received a doctorate from the Harvard Business School.
He had also been a prominent member of the Parti Québécois, serving as a staffer in René Lévesque's premier's office and holding a formal role in the pro-independence "Yes" side of the 1980 referendum.
The 65-year-old becomes the second Opposition Liberal MNA to quit in recent weeks, following Emmanuel Dubourg who resigned to run in a federal by-election.
Both are expected to claim severance pay.
Coalition Avenir Québec leader, François Legault, said he believes without Bachand, the Liberal Party's economic leadership is shaky.
"When I look at the remaining [Liberal] economic team, I'm very proud of mine and I don't think that [the Liberals] is a good team," said Legault.
Former premier Jean Charest called Bachand's departure a great loss.