Rob Summers, from Oregon, said standing on his own was “the most amazing feeling”.
He can voluntarily move his toes, hips, knees and ankles and also walk on a treadmill while being supported, according to research in the Lancet.
However, a UK expert said this should not be interpreted as a cure.
Rob was a keen baseball player and in 2006 was part of the team which won the College World Series.
But in that summer he was injured in a hit and run accident and his spinal cord was damaged.
Messages from the brain, which used to travel down the spinal cord, were blocked and he was paralysed.
Doctors surgically implanted 16 electrodes into his spine.
Rob trained daily in trying to stand, walk and move his legs, while electrical pulses were sent to the spinal cord.
Within days he was able to stand independently and eventually he could control his legs and step, with assistance, for short periods of time.
“None of us believed it,” said Professor Reggie Edgerton, from the University of California. “I was afraid to believe it.”
Rob has also regained other functions such as bladder, bowel and blood pressure control.
He said it had been a “long journey of countless hours of training” which had “completely changed my life”.
He added: “For someone who for four years was unable to even move a toe, to have the freedom and ability to stand on my own is the most amazing feeling.”
This study has proved that electrical stimulation works in one person. Four more patients are being lined up to further test the treatment.
Professor Geoffrey Raisman, from the Institute of Neurology at UCL, said: “This one case is interesting, and from one of the leading groups in the world. To what extent this procedure could in the future provide a further and sustained improvement cannot be judged on the basis of one patient.
“From the point of view of people currently suffering from spinal cord injury, future trials of this procedure could add one more approach to getting some benefit. It is not and does not claim to be a cure.”
Dr Melissa Andrews, from the Cambridge Centre for Brain Repair, said that while the study was a “little bit mind blowing” people should not say this is a cure.
She added: “I think people need to read this and say the possibility is out there, but it may not come tomorrow. It’s the closest we’ve ever seen and it’s the best hope right now.”
Professor Susan Harkema, who was part of the study at the University of Louisville, said: “It is really critical to be clear that it’s still in a research realm, but stay tuned we’re going to learn a lot more every day.”
For Rob he sees his story as a message of hope to people who are paralysed and as for walking again: “I see it as a major possibility.”