Comcast has abandoned its planned $45n (£30bn, €41.6bn) takeover of Time Warner Cable after regulators found that the deal would harm competition.
"Today, we move on," said Comcast chief Brian L Roberts. "We structured this deal so that if the government didn't agree, we could walk away."
Reports in US media in recent weeks had suggested that the Department of Justice (DoJ) would rule against the deal, after it launched an antitrust probe in March 2014.
If the deal had been approved, it would have created a cable and internet giant that served more than half of US homes with broadband speeds that meet the federal standard.
The decision is a blow to Roberts, who must renew efforts to find a workable business model for the internet and cable giant.
Amid falling numbers of subscribers and video customers, and facing growing competition from online competitors like Netflix, cable companies will likely still seek to merge in the coming months and years.