The six wheeled probed rolled off its landing platform onto Martian soil for a brief -- 78 second -- but intricately prepared three meter (10-foot) excursion.
The manoeuvre had been delayed because of problems with the airbag that had cushioned the landing of Mars Expedition Rover vehicle on January 3.
But Charles Elachi, director of NASA's Jet Propulsion Laboratory in Pasadena, California, triumphantly declared: "Spirit is now ready to start its mission of exploration and discovery."
Once off the platform, the robot only paused to realign its camera and transmission antenna before sending information, NASA officials said.
The first data confirming the success reached Earth an hour and 32 minutes after the order was given to start the drive. And six minutes after that, the first image of the landing vehicle taken by Spirit from the ground was at the mission headquarters. Champagne corks popped as the scientists waiting for word cheered.
"There was a great sigh of relief from me," said Kevin Burke, the lead mechanical engineer at Pasadena for the drive-off. "We are now on the surface of Mars."
The immediate objective is to analyze soil samples to detect the presence of water, which could determine if life once existed on Mars and provide future space missions a much needed source of fuel and oxygen.
NASA said that an international team of scientists at the laboratory would now decide how to examine the rocks, soil and atmosphere around Spirit.
"To our northeast, 250 meters (820 feet) to the northeast, is a crater 200 meters (655 feet) in diameter. This is an extremely attractive target," said mission scientist Steve Squyres, noting that it will "provide a window into the subsurface of Mars."
"The goal of this site is to try to find materials that will tell us whether or not Gusev crater once contained a lake and what the conditions were like in that lake," Squyres said.
Since landing on January 3, it has already beamed back colour images and other information about the terrain. NASA has been processing the images to make a high-resolution colour panorama from the most detailed images ever taken of the red planet.
The long-awaited spin on Martian soil came hours after US President George W. Bush announced that he wanted to send manned missions to the moon from 2015, and to Mars and beyond later.
The operation was conducted 12 days after the MER landed in the Gusev Crater.
Spirit's exit from the landing platform was delayed for three days because of problems with one of the airbags that cushioned the landing of the transport vehicle on Mars after a seven month journey from Earth.
NASA rotated Spirit 120 degrees to the right to stop it becoming entangled in the remains of the airbag.
A twin robotic probe, Opportunity, is set to land on another part of Mars on January 24.
Both are powered by solar energy and can move 40 meters (125 feet) each Martian day, more than during the entirety of NASA's 1997 Pathfinder mission, with its 10-kilogram (22-pound) mini-robot Sojourner.
Each robot will operate for three months on Mars.
On Friday, the European probe Mars Express will pass over Gusev crater, said Ray Arvidson, one of the US project scientists.
Mars Express may not be able to "see" Spirit, but the probe will take a series of measurements "looking down" that will prove helpful to the US mission, Arvidson said, praising the cooperative effort.