They travelled from steelmaking areas across Wales, Scotland and the north of England to take part in the demonstration in Sheffield.
Thousands of job losses have been announced in recent weeks in areas including Teesside and Scunthorpe, with unions fearing more will be lost soon.
Firms have blamed high energy costs and business rates affecting industries such as steel, made worse by cheap Chinese imports.
Roy Rickhuss, general secretary of the steelworkers’ union Community, told the rally that the steel industry was running out of time.
“The industry is suffering now. The time for Government action is now.
“We cannot give this Government even the smallest excuse to divert focus from delivering the urgent and meaningful action the industry so badly needs right now.
“We cannot allow our struggle for survival to be hijacked as a piece of political theatre. We must secure the rightful place of steelmaking at the absolute heart of an active industrial strategy.
“So we need action - not just words - on energy costs, business rates, skills retention and, most of all, action to ensure a level playing field
“Let us compete fairly - stopping, as the USA has done, the dumping of cheap steel from the likes of China.”
Louise Haigh, Labour MP for Sheffield Heeley, said: “It’s time for real action to save our steel.
“The Government’s short-sighted decision to refuse to support an industry which has been at the heart of our city and in communities across the country for generations is short-termism at its worst.
“Rather than wringing their hands and hiding behind EU law, they should be taking concrete action; immediately cutting business rates, leading international efforts to stop China dumping steel, using our world-renowned steel on British infrastructure projects.
“This rally is a demonstration of the values we in the trade union movement hold dear; and that message of solidarity should be heard loud and clear in Downing Street.”
TUC general secretary Frances O’Grady said: “The crisis in British steel isn’t over. One in six steelworkers face losing their jobs. Britain desperately needs a long-term industrial plan, but ministers have refused to commit to one.
“The closure of factories will devastate surrounding communities, and causes jobs losses throughout the supply chain. The Chancellor’s Northern Powerhouse has to be more than a slogan for a party conference.
“The North needs real support for job-rich industries with strategic economic value.
“British steelworkers contribute over £2 billion to our balance of trade. Every steelworker generates over £90,000 of added value. These aren’t jobs we can simply watch fade away.
“The US has taken strong steps to protect its steel industry, and so can we. I have written to the Prime Minister proposing international action to stop China dumping cheap steel on the global market.
“All we see from the Government is inaction at home, and inaction abroad. In the short run we need action on Chinese steel dumping. In the long run we need a serious industrial strategy.”
Dave Hulse, national officer of the GMB union, said: “The steel industry in the UK is in real crisis, with massive job losses taking place with the closure of the SSI plant in Redcar, redundancies in Tata Steel in Scunthorpe and the potential closure of the plants in Scotland on top of job losses which will take place in Rotherham and redundancies and closures in Caparo Industries.
“This rally is another step in the steel unions’ campaign to save jobs and force the Government to take action.
“If the unions had not mounted such a campaign, the Government would not have called the steel summit and would not have gone to Brussels to meet with the EU on the crisis. Their plan was to wring their hands and hope it would all go away.”
Business minister Anna Soubry said: “The Government is well aware of the challenges facing our steel industry and we are working tirelessly to help.
“On dumping we have taken clear action. In July, we voted for anti-dumping measures on Chinese wire rod imports and just last week voted for further anti-dumping measures on other steel products. It was the UK that helped persuade the European Commission to launch an investigation into steel rebar imports and the UK that secured an emergency EU council meeting this month.
“We will continue to do all we can to achieve a level playing field for our steel industry and workers.”