Medics rushed to the scene, but weren't able to revive him. He was identified as James Vanover, an engineer for United Space Alliance, a NASA contractor. Neither the company nor NASA released any details, including where he was working on the pad when the accident happened.
The chief executive officer of United Space Alliance, Virginia Barnes, said the company is providing full support to the accident investigation.
"Until that investigation is complete, it would be inappropriate to provide further comment on the details," she said in a statement.
NASA suspended work on the launch pad for the rest of the day.
Endeavour is due to blast off April 19 on its final flight. The shuttle arrived at the pad last week.
This is believed to be the first launch pad fatality since 1981, just before the very first shuttle launch.
The Associated Press contributed to this report.