A dozen more were injured, a rail official said.
Six of the people killed in the fiery crash were train passengers, and the seventh fatality was the female driver of the Jeep, the official said.
The collision happened about 7 p.m. when the gates at the two-track Commerce Street crossing near Valhalla came down on top of a Jeep Cherokee stopped on the tracks.
The driver got out to look at the rear of the vehicle, drove forward and was struck, a Metro Transit Authority official said. She was outside the vehicle when the train struck, the official said.
The 5:44 p.m. northbound train from Grand Central Terminal shoved the SUV about 10 car lengths.
The third rail pushed up from the track and rammed through the entire first car of the train. "Everything is melted inside," said Westchester County Executive Rob Astorino.
Photos of the scene and areal video from CNN affiliate WCBS
showed flames and smoke pouring out windows of the commuter train.
The commuter train was full when the accident happened. "There were about 650 (people) total on the ride home," said Astorino said.
A passenger, Justin Kaback, told CNN that people on his car didn't panic and exited in an orderly manner. Getting out of the car was difficult because it was so high and snow was on the ground, he said.
MTA said the riders evacuated themselves. About 400 commuters were taken to a rock-climbing gym for shelter, the train company official said. Buses were en route there to get to them to Pleasantville.
Twelve people were taken to Westchester Medical Center. Their condition was not immediately known.
The National Transportation Safety Board tweeted that the agency was sending a "go team" to investigate the crash.