Defence company Qinetiq said that the plane flew on autopilot for 82 hours 37 minutes, exceeding the current official world record for unmanned flight which stands at 30 hrs 24 mins set by Global Hawk in 2001 and Zephyr's previous longest flight of 54 hours, achieved last year. The Zephyr - "a high-altitude long-endurance Unmanned Aerial Vehicle (UAV)" - completed the test flight at the US Army's Yuma Proving Ground in Arizona.
The flight trial at Yuma took place between 28 and 31 July in the Sonoran Desert with temperatures up to 45C (113F).
Zephyr was flown on auto-pilot and via satellite communications to reach a maximum altitude of more than 60,000ft.
Launched by hand, Zephyr is an ultra-lightweight carbon-fibre aircraft that flies on auto-pilot, according to Qinetiq.
By day, it uses solar power generated by amorphous silicon solar panels no thicker than sheets of paper that cover the aircraft's wings.
At night, it is powered by rechargeable lithium-sulphur batteries, which are recharged during the day using solar power.
Qinetiq plans to continue developing the Zephyr over the next year to enable it to remain aloft for months at a time.