European Union spokeswoman Nabila Massrali had earlier congratulated Pezeshkian on his election, adding that the 27-member bloc is “ready to engage with the new government in line with EU policy of critical engagement”.
Pezeshkian is a heart surgeon whose only previous government experience was as health minister about two decades ago.
The death of ultraconservative president Ebrahim Raisi in a helicopter crash necessitated the election, which was not due until 2025.
Pezeshkian is considered a “reformist” in Iran, and was the only candidate from that camp allowed to stand in the election, for which all contenders were approved by Iran’s Guardian Council.
Iran’s supreme leader Ayatollah Ali Khamenei has the final say on all major policy issues in the country.
Under the hard-won 2015 deal, Iran agreed to freeze its nuclear programme in return for the lifting of the crippling international sanctions.
After the US withdrawal and reimposition of sanctions, Iran gradually began reneging on its own commitments to the agreement.
The parties to the 2015 deal with Iran saw it as the best way to stop the Islamic republic from building a nuclear bomb – a goal Tehran has always denied.
European Union members France and Germany were also party to the deal, along with Britain, China and Russia.
The European nations tried to salvage it, but Iran accused them of perceived inaction.