Police said the accident happened at 6am on the Bangkok-bound Asia highway in Tambon Ban Wa in Ayutthaya's Bang Pa-in district at 6am.
Sitthichai Sanamphan, 57, the driver of the Ban Mee-Bangkok van, died at hospital.
Police said the van hit the rear of a pickup truck driven by Chawalit Chaithip, 45, causing the pickup to flip.
Chawalit, who was not injured, said that he was steering his pickup the kerb towards after developing brake problems when it was hit by the van.
Police believe the van was speeding but they have yet to interrogate the passengers to establish the cause of the accident.