Modi's voice broke as he described his humble beginnings. "I came from a very poor family. ... We went to our neighbors' houses nearby (to) clean dishes, fill water, do hard chores. So you can imagine what a mother had to do to raise her children."
And Zuckerberg opened the event by telling Modi about a little-known incident several years ago when Facebook "wasn't doing so well." His then-mentor, the late former Apple Inc Chief Executive Steve Jobs, urged him to take a spiritual trip to India and visit a specific temple there.
That journey, Zuckerberg said, cleared his head and helped reaffirm Facebook's mission to connect billions of people around the world.
The Indian Prime Minister spent 50 minutes on stage with Zuckerberg, when he also talked about the importance of social media and his "Digital India" initiative, which seeks to connect thousands more Indian villages to the Internet and boost technology investments.
Modi did not offer any new announcements, but instead pointed to government programs aimed at combating problems and his administration's success in improving Internet accessibility.
Modi, 65, is the first Indian leader to visit the US West Coast in more than 30 years. His trip follows a similar visit by China's president, Xi Jinping, who met several tech leaders in Seattle last week.
Modi later visited Google headquarters and met with Indian-born CEO Sundar Pichai. Pichai announced that Google would bring wireless Internet to 500 Indian railway stations, news that Modi revealed at a dinner Saturday night.
He later travels to an event at the San Jose Convention Center that 18,000 people are expected to attend.
Facebook Chief Executive Mark Zuckerberg announced Modi's visit on his Facebook page earlier this month and invited users to post questions.
More than 46,000 comments were made in reply, with some questions regarding criticism that Modi did not do enough to stop 2002 religious riots in Gujarat that killed about 1,000 people, mostly Muslims, when he was chief minister of the state. He has vehemently denied any wrongdoing. No questions on that subject were brought up at the event.
Mostly Sikh protesters calling on Modi to answer for his human rights record temporarily blocked one of Facebook's entrances.
However, he generally received a rock-star welcome through most of his visit.
Modi boasts an 87 percent approval rating in India and is the second-most popular world leader on social media after US President Barack Obama.
© Thomson Reuters 2015