Leon said the government's case fell short on all counts and warned against seeking to delay the deal with an appeal saying that would cause irreparable harm to the companies.
The Justice Department's main argument against the merger was that by owning Time Warner's content, which includes must-have channels like CNN, AT&T could raise prices for pay-TV rivals and keep costs prohibitive for online streaming services.
The judge's ruling will likely be seen by tech and telecom giants as a green light to pursue a slew of major media acquisitions.
Now that the merger has been given the go ahead, AT&T will add Time Warner's content to its existing paid TV subscription. The Trump Justice Department sued to block the $85 billion merger, arguing that it would hurt competition in pay TV and cost consumers hundreds of millions of dollars more to stream TV and movies.
In making its case, the USA government argued that the merger of AT&T could harm consumers in a number of ways. Disney has bid $52 billion for most of 21st Century Fox's assets, and today's decision my determine whether Comcast makes its own offer, which could precipitate a bidding war.
Originally it was said that AT&T had planned to launch AT&T Watch no matter what happens with the current Time Warner DOJ court case.
This has been a long-running issue, as AT&T first announced its plans to buy Time Warner for $85.4 billion in 2016.
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Time Warner's sale could shape how much United States consumers pay for streaming TV and movies.
Months before Trump nominated him to the Justice Department's leading antitrust position in 2017, Delrahim even had expressed an openness to the combination of AT&T and Time Warner, predicting in an interview on Canadian television that it might not trigger any regulatory concerns.
Beyond the impact on the companies, the merger is expected to spur frantic dealmaking in the rapidly consolidating media sector.
Fans have been following the Disney/Fox deal closely, as a merger between the two companies would mean Marvel Studios would reacquire the rights to the X-Men and Fantastic Four franchises, both of which have been under Fox's control for decades. "We look 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".
AT&T has said that it was ready to close the deal and was just awaiting the judge's ruling in the case.
In this October 24, 2016, file photo, clouds are reflected in the glass facade of the Time Warner building in NY. That same day, Trump, then a candidate for president, pledged that his administration would block the deal. But Leon denied AT&T's request to disclose any communications between the White House and Attorney General Jeff Sessions about the merger and between Sessions and the department's antitrust division, keeping such speculation a mystery.