The La Marque Police Department said a truck headed west at a high speed on FM 1765 lost control and sideswiped another vehicle before careening into the parking lot of the Jack in the Box in the 4300 block of FM 1765 at about 4:30 p.m. on Saturday.
Investigators said after the truck hit another car in the parking lot, it rolled over and struck a trash bin structure.
Sgt. Richard Hernandez said both passengers in the truck were pronounced dead on the scene.
Those in the other car were taken to the hospital as a precaution, Hernandez said.
Police said at this point, speeding on a rain-slick road appears to be what led to the fatal crash.
The identities of those killed were not released as officials continued the investigation.