They worked with Andy Greenberg, a writer with tech website Wired, who drove the Jeep Cherokee on public roads in St Louis, Missouri.
Greenberg described how the air vents started blasting out cold air and the radio came on full blast when the hack began.
The windscreen wipers turned on with wiper fluid, blurring the glass, and a picture of the two hackers appeared on the car's digital display to signify they had gained access.
Greenberg said the hackers then slowed the car to a halt just as he was getting on the highway, causing a tailback behind him - though it got a lot worse after that. He wrote: "The most disturbing manoeuvre came when they cut the Jeep's brakes, leaving me frantically pumping the pedal as the 2-tonne SUV slid uncontrollably into a ditch.
"The researchers say they're working on perfecting their steering control - for now they can only hijack the wheel when the Jeep is in reverse.
"Their hack enables surveillance too: They can track a targeted Jeep's GPS co-ordinates, measure its speed, and even drop pins on a map to trace its route."
The hack was possible thanks to Uconnect, the software that has been built into the dashboard computers of hundreds of thousands of cars made by Fiat Chrysler Automobiles since late 2013.
The feature controls the entertainment system, deals with navigation and allows phone calls. It also allows owners to start the car remotely, flash the headlights using an app, and unlock doors.
But according to Miller and Valasek, the on-board internet connection is a "super nice vulnerability" for hackers. All they have to do is work out the car's IP address and know how to break into its systems and they can take control.
Independent security expert Graham Cluley said: "Note that the researchers believe that, although they've only tested it out on Jeeps, the attacks could be tweaked to work on any Chrysler car with a vulnerable Uconnect head unit."
The incident is the latest hacking episode which shows just how vulnerable we are to modern technology.
A US hacker also recently took control of a passenger jet he was on, in the first known such incident of its kind, according to the FBI. Chris Roberts is said to have plugged into the plane's computer systems through the electronics box under his seat - and briefly moved the aircraft sideways.
