The data shows not only that the supermassive black hole is accreting matter to itself at an extremely high rate, but also that the quasar may be producing up to 10,000 stars per year, scientists said.
Lead author Xiaohui Fan, from the University of Arizona, said he did not expect to find many quasars brighter than this in the entire universe.
He added: "That's something we have been looking for a long time".
Despite its brightness Hubble was only able to spot the quasar with the help of strong gravitational lensing caused by a dim galaxy between the quasar and the Earth.
The quasar was found in the constellation Taurus, which is close to the plane of the Milky Way galaxy.
The quasar was first imaged in multiple colors by two all-sky surveys, the UKIRT Hemisphere Survey and Pan-STARRS1.
"Quasar" is short for quasi-stellar radio source, and describes bright centres of galaxies.
"At such great distances, [quasars] are also extremely rare", said Laura Pentericci, an astronomer who studies distant galaxies at INAF Rome Astronomical Observatory but who was not part of the new study.
"We don't expect to find many quasars brighter than that in the whole observable universe". The astronomers next analyzed data showing the individual wavelengths emitted by the quasar.
The light from quasar J0439+1634, about 12.8 billion light-years away, bends as it passes by a galaxy roughly six billion light-years away.
The astronomers only came across it because of a galaxy in the foreground that acted as a gravitational lens - amplifying the ancient light from the quasar.
All galaxies have a supermassive black hole at their cores.
Astronomers said the quasar has a brightness equivalent to about 600 trillion suns and the supermassive black hole powering it is several hundred million times as massive as our sun. While the mass of the newfound quasar's black hole means it's large for the early universe, it's not among the biggest, Fan told Live Science. "Of course, we can only detect the big objects from that time, so nearly everything that we can detect from that era has to be pretty big".