Mohammad Javad Zarif met EU foreign policy chief Federica Mogherini ahead of evening talks with his counterparts from Britain, France and Germany - the three European signatories to the 2015 deal who are scrambling to preserve it.
Tehran has warned it is preparing to resume "industrial-scale" uranium enrichment "without any restrictions" unless Europe can provide solid guarantees that it can maintain the economic benefits it gained from the nuclear agreement despite the US reimposing sanctions.
Zarif gave an upbeat assessment after a "good and constructive" meeting with Mogherini.
"I believe we're on the right track to move forward in order to ensure that interests of all the JCPOA remaining participants, particularly Iran, will be preserved and guaranteed," he told reporters. The deal's official name is the Joint Comprehensive Plan of Action, or JCPOA.
But European diplomats have sought to play down expectations of Tuesday's meeting, stressing the enormous challenge of finding a way around US sanctions punishing foreign businesses trading with Iran, which have global reach.
"There is no one magic solution - there will be a complicated, comprehensive series of options at both the EU and national level, therefore it will take some time," a senior EU official said.
The European Union insists the deal is working, pointing to repeated UN inspections verifying the Islamic republic's compliance with its side of the bargain, and Mogherini's spokeswoman Maja Kocijancic told AFP ahead of Zarif's arrival that "we must do our utmost to preserve it."
EU leaders aim to show a united front on preserving the Iran deal when they meet for a pre-summit dinner in Sofia on Wednesday, officials said.
Mogherini and European Commission chief Jean-Claude Juncker will outline to the leaders what measures the bloc could take to shield its now substantial economic interests in Iran.
European firms, especially those from France and Germany, rushed to invest in Iran following the 2015 accord, under which Tehran agreed to freeze its nuclear program in return for the repeal of punishing international sanctions.
German exports to Iran totaled nearly 3 billion euros ($3.6 billion) in 2017, while French exports soared from 562 million euros in 2015 to 1.5 billion in 2017 and oil giant Total has pledged to invest some $5 billion in the South Pars gas field.