An investigation was under way to determine the cause of death, the Supreme Council for Delivery and Legacy, which is responsible for World Cup infrastructure, said in a statement.
The 40-year-old man died on Thursday at the Khalifa International Stadium, it said, without giving other details.
The Midmac-Six Construct joint venture said in a statement the accident occurred while the worker was on a suspended catwalk platform designed to manage technical functions relating to sound and light installations.
"One of the lever hoists supporting the platform failed, causing the fall of the worker, who was wearing all his safety equipment, including the safety harness. Sadly, the harness was cut during the fall with a fatal outcome," the company said, adding that it was investigating why the harness broke up.
Qatar's efforts to become the World Cup's first Arab host have been marred by accusations from human rights groups about abuse of workers, including allegations that they have been forced to live in squalor and to work without proper access to water and shelter in the blazing sun.
The Gulf Arab kingdom denies exploiting workers and says it is implementing labour reforms.
(Reporting By Tom Finn; writing by Maha El Dahan; editing by Mark Heinrich)
