Nearby planets like this are likely to be prime targets in the search for signatures of life, using the next generation of telescopes.
The planet's mass is thought to be more than three times bigger than our own, placing it in a category of world known as a "super-Earth".
It orbits Barnard's star, which sits "just" six light-years away.
The star is an extremely faint "red dwarf" that's about 3% as bright as the Sun.
Writing in the journal Nature, Guillem Anglada Escudé and colleagues say its newly discovered planetary companion has a mass 3.2 times bigger than the Earth's.
Dr Anglada Escudé said it was "possibly a mostly rocky planet with a massive atmosphere. It's probably very rich in volatiles like water, hydrogen, carbon dioxide - things like this. Many of them are frozen on the surface".