Libyan rebels demanding a greater share of oil wealth managed to load crude oil onto the ship, which escaped Libya's navy, embarrassing the government and prompting parliament to sack the prime minister.
US Navy Seals boarded the Morning Glory tanker in international waters off Cyprus on Sunday night and took control of the vessel, which the Pentagon said was held by three armed Libyans.
The tanker's seizure by US forces is likely to prevent more attempted oil sales by the rebels, who in August seized three terminals which had accounted for 700,000 barrels a day of exports.
No-one was hurt in the tanker raid, which was approved by US President Barack Obama and requested by the Libyan and Cypriot governments, Pentagon Press Secretary John Kirby said.
The stand-off over control of Opec member Libya's oil is one facet of wider turmoil that has engulfed the vast North African country since the civil war that led to the fall of Muammar Gaddafi nearly three years ago.
The tanker operation was the second time in six months that US forces have become involved in Libya. A commando team snatched an al Qaeda suspect off the street as he returned home from prayers in the capital Tripoli in September.