Royal held talks with the head of Iran's Environmental Protection Organisation, Massoumeh Ebtekar, and said they would build several key partnerships by February.
"Several highly operational subjects were discussed," Royal told reporters.
The French minister is travelling for three days with senior business figures from environmental and renewable energy firms specialising in water, pollution and energy efficiency - including the boss of multinational Engie.
"They were chosen by Iran on the basis of the challenges they face," said Royal.
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Royal said she would return in February to discuss progress on the partnerships.
Ebtekar, who is also a vice-president of Iran, said the visit "shows the important international cooperation on the environment, and sends a strong message to the global community that countries can cooperate strongly on their shared interests and issues in the field of environment."
Royal, who was wearing the headscarf that is obligatory in Iran, appeared reluctant to take too many questions from journalists in the wake of the recent uproar over the banning of burkini swimsuits in France.