Five days after taking over the majority in the chamber, House Democrats unveiled a bill that would significantly expand the requirements for background checks on gun sales.

In a major victory for gun control advocates, the legislation aims to close longstanding loopholes in federal law, which requires criminal background checks when guns are sold by licensed dealers but allows private citizens to sell and transfer guns to each other without any background check.

Closing these loopholes has been the top priority of the growing American gun control movement since the 2012 mass shooting at Sandy Hook elementary school, which left 20 children and six educators dead.

“Stopping gun violence takes courage – the courage to do what is right,” said the former Democratic congresswoman Gabrielle Giffords at an event on Capitol Hill. “We must never stop fighting. Fight. Fight. Fight,” she added, her speech slow but clear. Giffords survived being shot in the head exactly eight years ago in an attack that left six people dead. She now leads one of the country’s leading gun control groups.

The House speaker, Nancy Pelosi, who joined Giffords, said: “Today is also a day of action.” Pelosi recalled recalling hearing the news of Gifford’s shooting. “We say enough is enough by finally bringing bipartisan, commonsense background check legislation to the floor of the House.”

Also at the signing was David Hogg, one of the students who have advocated for reforms since the shooting at his Parkland, Florida, high school last year.

While the new bill – a top priority of the new House Democratic majority – is expected to pass the House, it is likely to be blocked from becoming law by the Republican-controlled Senate.

Still, even the partial passage of what Democrats are calling a “universal background checks bill” represents a significant step forward for American gun control advocates, as well as a sign of how far the Democratic party has moved to embrace gun control as a winning issue.

Early in the Obama administration, national Democratic leaders avoided getting involved in the gun control debate, following the Bill Clinton-approved strategy that saw gun control as the toxic “third rail” of American politics.

In 2016, after a mass shooting at an Orlando nightclub that left 49 people dead, House Republican leaders refused even to allow a debate on gun control legislation, prompting a dramatic protest by Democrats, who staged a 26-hour sit-in on the floor of the House of Representatives.

The Marjory Stoneman Douglas high school shooting survivor David Hogg attends the event on Capitol Hill. Photograph: Chip Somodevilla/Getty Images

The new legislation is significantly stronger and more comprehensive than the background check compromise that advanced after the Sandy Hook shooting, which would have closed the background check loophole for gun sales on the internet and at gun shows but left other private sales unregulated. That compromise failed to gain enough votes to overcome a potential filibuster in the Senate.

The stronger bill would not have seen the light without the continued activism by gun violence survivors, Peter Ambler, the executive director of Giffords’ gun control group, told the Guardian. “We’ll do everything we can to get this across the finish line,” he added.

“This is going to be a happy moment – a celebratory moment – and it allows us to see our hard work on the ground every single day actually being put into action,” said Jaclyn Corin, a Parkland student and one of the founders of March for Our Lives.

Student activists are already planning how they will fight for the passage of the legislation in the Republican-controlled Senate, Corin said.

“If they don’t support it or bring it to the floor, it really shows people that they value profits and money over their constituents’ lives,” she said.

Public opinion polls routinely find that overwhelming majorities of American voters, including Republicans and gun owners, support requiring background checks for all gun buyers. But the policy has been opposed by the National Rifle Association, gun manufacturers, and other gun rights advocates, who argue that increased legal regulations on gun buying is not an effective approach to deterring gun crime, and who also oppose most governmental regulation of guns on principle.

An estimated 22% of Americans who bought a gun in recent years did so without a background check, according to the best recent survey data. Nearly 40,000 Americans were killed with firearms in 2017, the majority of them gun suicides, according to statistics from the Centers for Disease Control and Prevention.