The rig, which had been working at the White Rose oilfield south of St. John's, was bound for Mississippi under tow when the line broke south of Newfoundland amid five-metre waves.
The rig was stranded for two days, while the crew of 99 rode out the storm until Friday morning when the line to the ship Atlantic Hawk was reattached.
The GSF Grand Banks was able to maintain its position by using its own thrusters.
"Our crews are trained to work in all kinds of weather conditions in Eastern Canada during drilling as well as during tows," said Guy Cantwell, a communications official with Transocean, which owns the rig.
"Everyone did a great job in terms of keeping the vessel and the people safe."
The GSF Grand Banks is again en route to a Mississippi shipyard, where it will undergo a scheduled refurbishment before returning to the oilpatch off Newfoundland.
The Transportation Safety Board said it has no plans to investigate the incident.
The GSF Grand Banks was damaged in 2011, when a supply vessel collided with it, putting a five-metre gash in one of its eight steel columns.