The former US president’s pages were suspended in the wake of the deadly January 6, 2021 insurrection attempt, in which his supporters stormed the US Capitol.
Meta, the parent company behind Facebook and Instagram, confirmed they lifted the ban, after saying last month it would happen “in the coming weeks”.
It said Trump would face heightened penalties of a suspension between one month and two years if he violated its content policies again.
Posts in which he questioned the outcome of the 2020 US presidential election remain up on both websites, despite having no basis in fact.
Supporters of the Republican, who is attempting another run for the presidency, have left messages welcoming him back.
Trump had been initially suspended indefinitely, but this was downgraded to a two-year suspension.
He had railed against the punishment, describing it as an “insult” to the millions who voted for him in the 2020 election, which he lost to Joe Biden.
Nick Clegg, the former UK MP and the company’s president of global affairs, said the public “should be able to hear what their politicians are saying”.
He said a review had found Trump’s accounts to no longer pose a serious risk to public safety.
The move will be helpful to the 76-year-old now amid his next run for the White House in 2024.
He had 23 million followers on Instagram and 34 million on Facebook as of January.