Justine Greening has called on the Tories to "dramatically change" saying her party has not properly connected with people in more than 30 years.
The ex-education secretary - who backs another EU referendum - said the party needs to "get into the centre ground".
And the Conservatives' "narrow" focus on Brexit had cost it votes at last year's election.
She laughed off suggestions she was launching a leadership bid, at another fringe meeting on Sunday.
Ms Greening, who quit the cabinet in January after refusing a move to the work and pensions department, has been working with businesses to boost social mobility.
The Putney MP said it had been 31 years since the last Conservative general election landslide and "31 years since we last truly carried the political argument in this country".
She praised Margaret Thatcher's government as one that was "radical" and one that "reached out" beyond core voters and re-shaped the future.
She said Labour leader Jeremy Corbyn and his grassroots support group Momentum were "attempting the same trick" and were succeeding "with more voters than any of us had imagined possible".
Ms Greening called on the Tory party to "recommit" to being "the party of opportunity," adding that they needed to see "the leadership and the strategy to deliver this".
She said a lack of opportunity for people led to the Brexit vote and called on her party to "step up to the plate" on social mobility.
The former cabinet minister said the government was not "set up for success" and took aim at her old department saying the Treasury "doesn't put a value… on educating our children better, it doesn't have a framework for properly valuing investment in people".
At an earlier fringe meeting on Sunday, one audience member called for the Conservative leadership to "skip a generation" next time and to go to a younger candidate.
This was jokingly dubbed the launch of Ms Greening's leadership campaign by Tory grandee Lord Willetts.