"I'm incredibly grateful to the jury for working so hard on this case ... and to my lawyers ... and to my family and friends and so many other people who supported me," Kennedy said afterward. "I'm happy justice was done."
Kennedy is a human-rights advocate, ex-wife of New York Gov. Andrew Cuomo, a daughter of Sen. Robert F. Kennedy and a niece of President John F. Kennedy.
Authorities say she struck a tractor-trailer on Interstate 684, and then took an exit off the highway before her car became disabled on July 13, 2012. Officers found her slumped at the steering wheel.
The 54-year-old Kennedy said she took a sleeping pill by mistake instead of her thyroid medication. She testified that the drug overpowered her and she doesn't remember the crash. A blood test showed that a toxicologist detected 14 nanograms per milliliter of zolpidem, the sleep aid found in Ambien. Doctors said the amount was typical of someone who just took a pill or had taken one several hours before.
The prosecutor's office issued a statement following the verdict, saying "the jury heard all the evidence in this case and we respect their verdict."
The Associated Press contributed to this report.