The Jackson Building Centres driver was making a delivery in Corby on Tuesday morning when the accident happened.
Paramedics pronounced him dead at the scene.
A spokesman for the company said it was co-operating with the police and the Health and Safety Executive (HSE), which confirmed it was investigating.
Lyndon Johnson, the company’s divisional director, told the BBC: “This is a tragic accident and the shock is felt very deeply by all of us here.
“Our thoughts and sympathies now lie with his family, friends and colleagues.”
The man has not yet been named, and no further details about the accident have been released.