Modi's voice broke as he described his humble beginnings. "I came from a very poor family. ... We went to our neighbours’ 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".
That journey, Zuckerberg said, cleared his head and helped reaffirm Facebook's mission to connect billions of people around the world.
The Indian premier 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.
He later travels to an event at the San Jose Convention Centre 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.
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.
On Saturday, he attended a dinner with 350 business leaders where Indian-born CEOs Satya Nadella of Microsoft Corp, Shantanu Narayen of Adobe Systems Inc and Pichai of Google moderated a panel.
Modi visited Tesla Motors headquarters on Saturday and met Chief Executive Elon Musk, where the two discussed renewable energy. He also met Apple Inc Chief Executive Tim Cook.