The new world, Kepler-1647b, is the largest known to orbit two stars, like the fictional planet Tatooine in the Star Wars movies.
It is one of more than 1,200 extrasolar planets detected so far by the US space agency Nasa’s Kepler space telescope.
Astronomers found it by studying the tiny dip in light that occurred when the planet moved in front of, or transited, its parent stars.
Nearly half of all sun-like stars are in gravitationally-bound binary systems, but to date only nine planets orbiting paired stars have been discovered by Kepler.
All those previously found have been Saturn-sized or smaller, and tended to orbit close to their host stars.
Kepler-1647b has an orbital period of three years, the longest of any confirmed transiting planet.
In addition, it lies within its host stars’ habitable zone - the orbital band in which temperatures are mild enough to allow liquid surface water, and potentially, life.
Although the planet itself is too large to be habitable, it could have moons that support life, the scientists believe.
Astronomer Dr Nader Haghighipour, from the University of Hawaii, said: “A giant planet similar to those in our solar system may well host undetected large moons that could be habitable.”
Kepler-1647b, which lies in the direction of the constellation Cygnus, is believed to be around 4.4 billion years old - roughly the same age as the Earth.