Web Summit has decided to go fully online this year and said it will host 100,000 attendees online on its own conference platform on December 2-4.
It said the decision to move fully online in the interests of public health follows discussions with the Portuguese government and city of Lisbon.
Web Summit 2020 will be the second event hosted on the platform, following the Collision from Home event this June, which featured more than 30,000 online attendees.
"Lisbon is still Web Summit's home, but with growing Covid-19 outbreaks across Europe, we have to think of what's best for the people of Portugal and our attendees," Web Summit chief executive Paddy Cosgrave said.
"The safest and most reasonable answer is to host Web Summit fully online in 2020. We look forward to welcoming attendees back to Lisbon in 2021," he added.
About 800 speakers will join this year's event online.
These include Zoom founder and CEO Eric Yuan, European Commissioner Margrethe Vestager, Captain America star Chris Evans, Facebook CTO Mike Schroepfer and scientist and conservationist Jane Goodall.
More than 500 companies have already confirmed they will exhibit online at Web Summit, including Cisco Systems, Siemens, UBS, Twilio and Cloudflare.
In 2016 Web Summit moved from Ireland to Lisbon for an initial period of three years, but it has since expanded that deal to run up to 2028.
Founded in Dublin in 2010 as a technology-focused conference, Web Summit it has rapidly grown into one of the world's largest conference events of its kind and now includes a variety of subject areas in its programme.
It also runs events in Asia and the US.