The Trump administration had ordered the ban on downloads of video-sharing app TikTok as well as messaging platform WeChat, both owned by Chinese companies.
A California court ruling said it granted the “motion for a nationwide injunction against the implementation” of the government order, with the judge citing concerns over free speech.
The order against WeChat would have slowed it down and made it unusable in the United States for videochats with family and friends, according to experts.
Owned by technology giant TenCent, WeChat in the United States has around 19 million active daily users.
President Donald Trump said Saturday that he had approved a deal allowing Silicon Valley giant Oracle to become the data partner for hugely popular TikTok to avert a shutdown of that app.
The deal, announced by the companies, includes Walmart as a commercial partner and would create a new US company named TikTok Global.
TikTok — owned by China’s ByteDance — confirmed the agreement, which came with companies racing against the Sunday deadline set by Trump’s administration.
The US Department of Commerce on Saturday announced it was postponing the ban on TikTok downloads until September 27, due to “recent positive developments.”
When announcing the ban on Friday, Commerce Secretary Wilbur Ross had said China used the two apps “to threaten the national security, foreign policy, and the economy of the US.”