The discovery provides the first evidence that terrestrial planets can form in orbits similar to the Earth, even in a binary star system where the stars are not very far apart.
At twice the mass of the Earth, the planet orbits one of the stars in the binary system at almost exactly the same distance from which the Earth orbits the sun.
However, because the planet's host star is much dimmer than the sun, the planet is much colder than the Earth - "a little colder, in fact, than Jupiter's icy moon Europa."
"Although this planet itself is too cold to be habitable, the same planet orbiting a sun-like star in such a binary system would be in the so-called 'habitable zone' - the region where conditions might be right for life," said Scott Gaudi, a professor of astronomy at Ohio State University.
This greatly expands the potential locations to discover habitable planets in the future.
"Half the stars in the galaxy are in binary systems. We had no idea if Earth-like planets in Earth-like orbits could even form in these systems," he added.
The planet, called OGLE-2013-BLG-0341LBb, first appeared as a "dip" in the line tracing the brightness data taken by the OGLE (Optical Gravitational Lensing Experiment) telescope.
This detailed analysis showed that the planet is twice the mass of the Earth and orbits its star from an Earth-like distance of around 90 million miles.
"This discovery suggests that there may be many more terrestrial planets out there - some possibly warmer, and possibly harbouring life," said professor Andrew Gould of the Ohio State University in a paper published in the journal Science.