Illinois Democratic congressman Dan Lipinski, who has served since 2005, has been defeated by a progressive primary challenger in a stunning victory for the party’s left wing.

Mr Lipinski, representative for Illinois’s third congressional district – a safe Democratic seat – was defeated by Marie Newman, an entrepreneur and nonprofit founder who supports progressive proposals such as Medicare for All and a $15-per-hour minimum wage. With nearly 99 per cent of the vote counted, she led Mr Lipinski by some 2,365 votes.

Ms Newman’s victory echoes the rise of Alexandria Ocasio-Cortez, now a progressive hero, who defeated senior Democrat Joe Crowley in her district’s primary in 2018. She has this year started a political action committee to support left-wing candidates across the country – Ms Newman among them.

Progressive Democrats have long taken a dim view of Mr Lipinski, who has spoken out against LGBT+ rights and voted against Obamacare. Most of all, they take exception to his voting record on abortion rights: he has voted to de-fund Planned Parenthood and to ban abortions at 20 weeks or more, and served as chair of the Congressional Pro-Life Caucus.

With the Supreme Court tilting right thanks to Donald Trump’s two appointees, pivotal cases are increasing the likelihood that Roe vs Wade could be all but overturned. In this climate, the Democratic Party is less inclined than ever to put up with pro-life voting among its members of Congress.

Tweeting her joy at the result, Ms Newman promised to press on with the progressive agenda that has gathered steam in the party in the last few years.

“I am bursting with pride and gratitude for the amazing coalition that helped bring about much needed change in our district. We are going to work together to lower health care costs, to fight climate change, and to build an economy that works for everyone.”

Ms Newman won her insurgent victory on the same night as the Illinois presidential primary, in which Joe Biden triumphed over Bernie Sanders by 23 points. Mr Biden is now essentially guaranteed to be the Democratic nominee.