It happened just before 11 p.m. near Beltway 8 in southeast Houston.
Witnesses told officers they saw the man fall out of the bed of a white pickup truck, which continued traveling after it happened, according to Houston police.
It appeared the victim died from the impact of falling out of the truck and was not struck by passing vehicles, investigators said. The man's identity wasn't immediately released.
"He was in the bed of a truck, and either the driver swerved, and he was intoxicated and he fell out, and now we have a person that passed away," said Lt. Emanuel Pavel with Houston police.
The pickup truck had not yet been located as of Sunday morning.