However, the robot has not found any direct traces of living organisms, NASA scientists announced.
A study of a fine, layered rock by the rover detected evidence of sulphates and other minerals that form in the presence of water.
The finding suggests that, if there had been life present, when the rocks were formed, then the living conditions could have permitted an organism to flourish.
The study, however, has found no direct evidence of life.
Lead NASA scientist James Garvin said: "NASA launched the Mars Exploration Rover mission specifically to check whether at least one part of Mars had a persistently wet environment that could possibly have been hospitable to life.
"We have strong evidence for an exciting answer: Yes."
Scientists have long believed that for at least half its 4.6bn-year-life, Mars was home to life.