The man died during work in a lift shaft and was pronounced dead at the scene by the emergency services.
Work resumed this morning after the site was closed for the weekend following the incident. An investigation is underway.
A BAA spokesman said: “Our thoughts are with the worker's family and friends at this very sad time.”
It was the second fatality on the £4.3 billion project since it started five years ago.
Ucatt general secretary Alan Ritchie said: “This tragedy demonstrates the dangerous nature of the construction industry and underlines why the highest level of safety must be adhered to at all times.”
The new terminal is due to open next March.