Dominion Voting Systems has filed a $1.6bn (£1.2bn) defamation lawsuit against Fox News, arguing it promoted baseless claims of vote-rigging.
Conservatives and Trump campaigners had claimed last year that the US company had altered its voting machines to deny re-election to Donald Trump.
The false claim of a stolen election was promoted by Mr Trump and helped fuel the 6 January attack on Congress.
Fox News said it would fight the "baseless lawsuit in court".
The lawsuit argues that Fox News, which hosted guests touting anti-Dominion conspiracy theories during the 2020 election, "recklessly disregarded the truth" because "the lies were good for Fox's business".
"Fox News Media is proud of our 2020 election coverage, which stands in the highest tradition of American journalism, and we will vigorously defend against this baseless lawsuit in court," the media company said in its response.
Dominion is one of the largest manufacturers of voting equipment in the US. Its machines were used by at least 28 states in last November's election.
There is no evidence for widespread voting fraud in the presidential election. The fraud argument has been refuted by courts across the US, as well as Trump-appointed judges and his own attorney general, William Barr.
Among those spreading falsehoods about Dominion was long-time Trump lawyer Rudy Giuliani and lawyer Sidney Powell, who also worked for the campaign.
One claim made by the pair was that Dominion, a US company founded in 2002, had worked with late Venezuelan leader Hugo Chavez to create machines that would "make sure he never lost an election".
This is the second election-related lawsuit to hit Fox News.
Smartmatic, another election technology company, sued Fox Corporation and several top presenters for $2.7bn in January over similar claims.
Earlier this week, lawyers for Ms Powell argued in court that her claims that "Democrats were attempting to steal the election and had developed a computer system to alter votes electronically" were clearly an exaggeration and protected political speech.
"No reasonable person would conclude that the statements were truly statements of fact," her team argued in an attempt to dismiss Dominion's separate lawsuit against her.