It measures 40 billion km across - three million times the size of the Earth - and has been named by scientists as "a monster".
The black hole is 500 million trillion km away and was photographed by a network of eight telescopes across the world.
Details have been announced today in Astrophysical Journal Letters.
Prof Heino Falcke, of Radboud University in the Netherlands, who suggested the experiment, told BBC News that the black hole was found in a galaxy called M87.
"What we see is larger than the size of our entire Solar System," he said.
"It has a mass 6.5 billion times that of the Sun. And it is one of the heaviest black holes that we think exists. It is an absolute monster, the heavyweight champion of black holes in the Universe."
The image shows a very bright "ring of fire", as Prof Falcke describes it, surrounding a perfectly circular dark hole. The bright halo is caused by superheated gas falling into the hole. The light is brighter than all the billions of other stars in the galaxy combined - which is why it can be seen at such distance from Earth.