The partnership comes after NASA pulled out of the ExoMars program with ESA last year due to budget cuts.
ESA said in a statement Thursday that it and Roscomos aim to launch missions in 2016 and 2018 to try to establish whether life ever existed on Mars.
The two sides have agreed to a “balanced sharing of responsibilities” and will cooperate on scientific research.
Among ESA’s contributions will be the ExoMars rover, which is being built for the 2018 mission to search the planet’s surface for signs of life and able to drill to depths of two meters.
The rover will be delivered by a Russian descent module.