US District Court judge Richard Leon has approved AT&T's $85B deal to acquire Time Warner, a transaction opposed by president Trump.
He ruled the transaction would not violate antitrust laws.
The Justice Dept. claimed the mega-merger would squash competition in the pay TV business.
The ruling is expected to trigger a wave of further consolidation in the media business.
Comcast, for instance, has said its all-cash $60B bid for 21st Century Fox was contingent on AT&T's getting the federal green light for its Time Warner acquisition.
Walt Disney Co. has a $52B deal to acquire 21CF.