"Glad to have seen a friend and a great leader, Barack Obama, in Milan," Renzi wrote on Facebook, reiterating the pair’s close bond which has developed over the years.
According to Italian news agency ANSA, the two former heads of government greeted each other affectionately before sitting down to discuss Europe and the current international political climate.
After a two-hour talk, the duo left the hotel in the same car to attend the Higher Institute for International Policy (ISPI), where they dined with 16 Milanese entrepreneurs and businessmen.
The pair received applause from a small group when they arrived at the event, before being rushed indoors.
Obama was in Milan for two days, speaking on climate change, innovation and food security at a global food conference on Tuesday.
