"Heartiest congratulations to my friend, President @HassanRouhani on his re-election," Modi tweeted in English and Persian languages.
"India remains committed to strengthening our special relationship with Iran," he added.
The Prime Minister expressed confidence that Iran will continue to achieve new heights under the dynamic leadership of President Rouhani.
Rouhani, a 68-year-old cleric, won a resounding re- election victory today as voters backed his efforts to rebuild foreign ties and kickstart the struggling economy.
He defeated 56-year-old hardline cleric Raisi, who had had positioned himself as a defender of the poor and called for a much tougher line with the West.