It might have taken the robot 11 years and two months but it represents a significant landmark for NASA.
"This is the first time any human enterprise has exceeded the distance of a marathon on the surface of another world," said John Callas, Opportunity project manager at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.
"A first time happens only once."
It beat out previous record-holder, the Soviet-era Lunokhod 2 moon rover in the distance stakes.
"This mission isn't about setting distance records, of course," said Cornell University's Steve Squyres, the Opportunity mission's principal investigator. "Still, running a marathon on Mars feels pretty cool."
Water discovery
The plucky rover-that-could has long exceeded expectations, arriving on the Red Planet on January 25, 2004, with an "original three-month prime mission."
Within months of beginning its Martian mission, Opportunity had discovered evidence of both running and groundwater on the mostly barren planet.
Opportunity is currently on the rim of the huge Endeavor crater, which it has spent the last four years traversing. It sits now in Marathon Valley, named after the rover's achievement.
Along with its sister rover Curiosity and three Mars orbiters, it will seek to understand more about our nearest planetary neighbor, including "its present and past environment, climate cycles, geology and biological potential," NASA said in a statement.
NASA's previous Martian resident, the Spirit rover, ceased communication with ground control in 2010.
The space agency is also working to develop human spaceflight capabilities for a manned mission to Mars.
The rover team in Pasadena is planning a marathon-length relay run next week to celebrate Opportunity's landmark.
