As the most luminous non-transient objects, distant quasars are important tracers to study the formation of the earliest supermassive black holes (SMBHs) and the history of cosmic reionization. Despite extensive efforts, only two quasars have been found at z>=7.5 previously, due to a combination of its low spatial density and high contamination from much more numerous Galactic cool dwarfs in quasar selection. We report the discovery of a luminous quasar at z=7.64, the most distant quasar yet known. This quasar has a bolometric luminosity of 3.6×1013 Lsun. Near-infrared spectroscopic observations reveals a SMBH with a mass of 1.6 billion Msun inhabiting the center of this quasar. The existence of such a massive SMBH just 670 million years after the Big Bang significantly challenges theoretical models of SMBH formation and growth. In addition, strong active galactic nucleus (AGN) driven wind already in place in this system, as evidenced by the relativistic outflows with a maximum velocity speed close to 20% of the speed of light and the strongly blueshifted CIV emission line in the quasar spectrum. Therefore this record-breaking quasar provides a unique laboratory to investigate AGN feedback on the formation and growth of the most massive galaxies in the early universe.