Sir Tim, who invented the World Wide Web in 1989, called for a "revolution" in how the internet is regulated and monetised in order to stem abuse, political polarisation and fake news.
The 63-year-old was speaking at the Web Summit in Lisbon to launch a new "contract for the web" which asks internet companies to uphold a set of principles such as protecting privacy and being transparent about their algorithms.
Facebook and Google have backed the contract, which will be agreed in detail next year, despite both companies being mentioned by its creator as examples of how "the web we know and love" is under threat.
Sir Tim said: "For the first 15 years, most people just expected the web to do great things. They thought 'there'll be good and bad, that is humanity, but if you connect humanity with technology, great things will happen....