"This was a defining case for antitrust enforcement in the U.S.", former Justice Department antitrust attorney Ketan Jhaveri said.
David McAtee, AT&T general counsel, said: "We are pleased that, after conducting a full and fair trial on the merits, the court has categorically rejected the government's lawsuit to block our merger with Time Warner".
Other media stocks that saw big price moves after the judge's ruling was announced included 21 Century Fox (FOX), whose shares were up almost 5 percent on speculation it could be the subject of a bidding war between Disney (DIS), which already has a $52 billion all-stock deal for Fox on the table, and a media giant like Comcast (CMCSA), which in recent weeks has been hinting of its intention to make an even larger all-cash bid for Fox.
The merger, which is set to be completed June 21, would create a massive new media company, combining AT&T's cable TV, satellite TV, and cellular telephone networks with the media giant that owns the Warner Bros. movie studio as well as the cable TV channels CNN and HBO.
The Justice Department could seek a stay of his decision, essentially freezing the combination of the two companies while the case works its way through the appeals process. "For AT&T and Time Warner, this is a major victory lap".
Late past year, AT&T confirmed that the DOJ was seeking to block the merger and AT&T CEO Randall Stephenson signaled his company's intent to fight back against the challenge. But AT&T and Time Warner have said they will begin to merge the companies as soon as possible.
The ruling potentially closes a deal that was originally announced in October 2016.
Leon said the government failed to prove that the merger would lead to higher prices and other ham to consumers.
The Writers Guild of America West called Leon's decision a "blow to consumers, content creators and competition".
Nadal joins '$100m club' after French Open win
But as Nadal's uncle, Toni Nadal, said shortly afterwards, "this is not normal". "I want to say well played to Dominic. The Spaniard got early breaks in the second and third set, to keep a battling, but baffled, Thiem at bay.
Number three wireless carrier T-Mobile, meanwhile, is seeking a tie-up with number four Sprint.
"Common sense tells you that this degree of concentrated power isn't right", wrote Zephyr Teachout, a candidate for attorney general of NY, wrote immediately following the judge's ruling.
The US had sued to block the deal, arguing that it would reduce competition in pay TV and lead to higher prices for consumers. Time Warner and AT&T avoided invoking the president's statements before and during the trial, and the judge barred them from obtaining White House communications to introduce in the trial, stating in March that the companies had "fallen far short of establishing that this enforcement action was selective". Comcast and Verizon are also jockeying for position in the new landscape.
Otherwise, AT&T will take control of the Time Warner assets in about a week. That same day, Trump, then a candidate for president, pledged that his administration would block the deal.
The merger brings together AT&T's data and distribution pipeline with Time Warner's vast content library as the combined company competes with tech giants like Facebook, Amazon, Apple, Netflix, and Google - also known as FAANG.
"There have been lots of cases where judges say insane things in court and the ruling came out different than you'd expect", he said.
Attorneys for AT&T and Time Warner argued that it would be absurd for them to deny their shows to millions of viewers, because it would cost them millions in lost broadcast fees and advertising revenues.
And ultimately that's what worked.
AT&T Attorney Daniel Petrocelli said the companies were frustrated that the resolution took 18 months, but were relieved the fight was finally over.