The meeting also assumes significance as it comes in the wake of a major jolt to the global fight against climate change with US President Donald Trump announcing to withdraw America from the Paris Climate Accord.
"Had a very good meeting with @UN Secretary-General, Mr. @antonioguterres," Modi said in a tweet after the meeting.
"Stressing multilateralism to address global challenges such as terrorism. PM @narendramodi receives UNSG @antonioguterres in St Petersburg," External Affairs Ministry spokesperson Gopal Baglay tweeted along with a photo of the meeting.
He also met his Mongolian counterpart J Erdenebat.
Modi said he held wide-ranging talks with Erdenebat during their interaction on the sidelines of the SPIEF.
Earlier today, Modi attended the SPIEF where he made a strong pitch to global businesses for investing in India, saying its market of 120 crore people provides vast opportunities from agriculture to defense, while being protected by political stability and a "vibrant" judicial system.