US officials and lawmakers in recent weeks have voiced fears of the wildly popular video platform being used by Beijing for nefarious purposes.
However, the company has denied any links to the Chinese government.
Media reports circulated yesterday saying that Trump would require the US operations of the app be divested from its Chinese parent firm ByteDance, but the president announced a ban.
Speaking to reporters on Air Force One, Trump said: "As far as TikTok is concerned, we're banning them from the United States."
He added he would take action as soon as today using emergency economic power or an executive order.