The adviser, Emmanuel Bonne, held “high-level meetings” Wednesday in Tehran, “with the aim of contributing to the de-escalation of tensions in the region”, Macron’s office said.
The presidency refused to say whom Bonne met, adding only that he left Tehran on Wednesday evening.
On Thursday, Iran announced that it had shot down a US “spy drone” that violated Iranian airspace near the Strait of Hormuz.
Tensions between the longtime foes have increased sharply since US President Donald Trump last year abandoned a landmark 2015 nuclear agreement with Iran and re-imposed sanctions.
Macron, who is travelling to a G20 summit in the Japanese city of Osaka on June 28-29, will “have contact with the main players” in the standoff, his office said.
Before that he will pay an official visit to Japan on June 26-27, during which he will hold talks with Prime Minister Shinzo Abe, who recently travelled to Iran to try mediate in the crisis.
Abe met with Iran’s supreme leader, Ayatollah Ali Khamenei, who categorically refused to hold talks with Trump.