AT&T has been given the green light for its $85bn (£63bn) blockbuster takeover of Time Warner, rebuffing efforts to block the deal by the Trump administration.
Judge Richard Leon said the proposed takeover could go ahead without any conditions, rejecting the US Justice Department's arguments that it would limit competition and mean higher prices for pay-TV subscribers.
He said parts of the government's case had been "gossamer thin" and "plagued by inconsistencies". In conclusion, he said, "the government has failed to meet its burden of proof".
It will come as a major blow to the Department's antitrust head Makan Delrahim, whose decision to sue came as a surprise to many given the two companies are not direct competitors and the deal would be a vertical merger.
AT&T is a telecommunications company while Time Warner is an entertainment business, behind hit shows such as Game of Thrones.
However, the attempt to stop the takeover had got the backing of the president, who had been vocal in his opposition to the deal during his 2016 campaign, saying it was "not good for the country".
CNN’S slogan is CNN, THE MOST TRUSTED NAME IN NEWS. Everyone knows this is not true, that this could, in fact, be a fraud on the American Public. There are many outlets that are far more trusted than Fake News CNN. Their slogan should be CNN, THE LEAST TRUSTED NAME IN NEWS!— Donald J. Trump (@realDonaldTrump) December 9, 2017
Although Mr Trump has previously claimed he played no part in the action to block the deal, his legal advisor Rudy Giuliani said he had "denied the merger", and some have speculated his opposition to AT&T's takeover was politically motivated given his strong criticism of Time Warner's news channel CNN throughout his presidency.
However, the Justice Department had focused on its argument that the deal would lead to fewer choices for consumers during the case, and Mr Delrahim had argued that "politics plays no role in our law enforcement of antitrust cases".
Why doesn’t the Fake News Media state that the Trump Administration’s Anti-Trust Division has been, and is, opposed to the AT&T purchase of Time Warner in a currently ongoing Trial. Such a disgrace in reporting!— Donald J. Trump (@realDonaldTrump) May 11, 2018
After the judgment, Mr Delrahim said: "We are disappointed by the court's decision today.
"We will closely review the court's opinion and consider next steps in light of our commitment to preserving competition for the benefit of American consumers."
AT&T general counsel David McAtee said the company looked forward to closing the merger on or before June 20 "so we can begin to give consumers video entertainment that is more affordable, mobile and innovative".
Daniel Petrocelli, the company's lead trial attorney, said there would be no divestment of any assets once the deal completes.
The ruling is likely to prompt a flurry of major tie-ups in the media industry. Sources familiar with the matter told The Daily Telegraph that Comcast is set to formally submit an offer for 21st Century Fox's assets on Wednesday.
Comcast, AT&T's biggest rival, last month said it was in advanced stages of preparing a rival bid for the clutch of assets 21st Century Fox has agreed to sell to Disney, and its expected decision to submit a formal offer is likely to spark a bidding war with Disney.
It is thought the ruling will not only lead to rapid consolidation in the media industry, but could also prompt technology companies such as Facebook to undertake their own vertical deals, after having learnt the court will disregard government efforts to stop them.