The dramatic reversal came hours before the strikes were expected to be carried out.
But details of the diplomatic breakthrough after more than three months of war - including how Iran's leadership had signalled its approval - were not immediately clear in Trump's post on Truth Social.
"Based on the fact that discussions with the Islamic Republic of Iran have been brought to the highest level of Iranian leadership and approved, I have, as President of the United States of America, cancelled the scheduled strikes and bombings against Iran this evening," Trump wrote.
"Discussions and final points have been, in both concept and great detail, approved by all parties involved, including the United States, Israel, Saudi Arabia, UAE, Qatar, Turkey, Pakistan, Bahrain, Kuwait, Jordan, Egypt, and others. The Naval Blockade will remain in full force and effect until this Transaction is finalised - Time and place of the signing to be announced shortly," he added.
"The Naval Blockade will remain in full force and effect until this Transaction is finalised - Time and place of the signing to be announced shortly," he said.
There was no immediate comment from Iran.
Trump's post marked a sharp about-turn from a previous post where he said the US could take Kharg Island, Iran's main oil export terminal.
The latest apparent breakthrough after stalled efforts to end the war came as clashes took the shaky two-month truce to the brink.
Iran's foreign ministry said the US attacks had "effectively rendered the ceasefire … meaningless" but notably stopped short of saying it was abandoning it.
Central to the negotiations has been Iran's stranglehold on the Strait of Hormuz, which has disrupted oil and gas supplies and driven up fuel and food prices.
with PA
