TikTok temporarily shut down in the US as a Supreme Court-upheld ban took effect, affecting 170 million American users.
President-elect Trump promised to issue an executive order to delay the ban's implementation, reversing his previous stance.
ByteDance voluntarily suspended US operations before the Sunday deadline, after failing to sell its US operations as required by law.
TikTok CEO Shou Zi Chew thanked Trump for providing "clarity and assurance" as services began restoring.
The bipartisan law required ByteDance to sell TikTok's US operations or face removal from app stores and web hosting services.
The Supreme Court unanimously upheld the ban, citing national security concerns about data collection and China ties.
Trump proposed a 50% US ownership position in a joint venture, claiming it could make TikTok worth "hundreds of billions."
The ban created a rift between Trump and fellow Republicans, including incoming Secretary of State Marco Rubio.
TikTok displayed a shutdown message to users, while removing the app from Apple and Google Play stores.
The law includes penalties for companies helping TikTok operate, with a five-year statute of limitations.