This will be the first ever direct route connecting the two cities and the only current nonstop flight from the US to Singapore.
United will use Boeing 787-9 Dreamliner jets on the 8,446 mile route, which it says is the longest scheduled 787 flight operated by any US carrier.
"We are very excited about introducing nonstop flights between San Francisco and Singapore," said Marcel Fuchs, United's vice president of Atlantic and Pacific sales.
"This long-awaited service has been made possible by the newest version of our customer-pleasing Boeing 787 Dreamliner. Customers arriving to San Francisco will have dozens of options to connect to other cities across the Americas."
With the launch of flights on June 1, 2016, United will discontinue its current Singapore-Tokyo Narita service.
The route will continue to be served by trans-Pacific joint venture partner All Nippnon Airways.
San Francisco to Singapore Stretcher patient travel possible