West Yorkshire Police said a woman had been seriously injured when she fell from the overhead Tunstall Road Bridge this morning.
It prompted a significant emergency services response, with the anticlockwise carriageway fully closed to traffic for more than an hour.
Initial reports from Highways England had suggested that there was a serious collision on the major route into the city.
But a police spokesman later said: "Emergency services were called to the M621 at Hunslet at about 7.16am this morning following a reports a woman had fallen from the overhead Tunstall Road Bridge onto the carriageway.
"Police and ambulance attended and the woman was taken to hospital for treatment to injuries which are serious but not thought to be life-threatening.
"Road closures were put in place with diversions signposted, but the M621 has now fully re-opened."
The spokesman said enquiries into the incident were ongoing.