Westport police say 18-year-old Ellis Tibere, of Guilford, was charged with attempted murder and other offenses in connection with the Monday attack.
The 33-year-old victim was sitting in her car prior to an appointment when someone with a knife and wearing a mask opened the door.
She was stabbed in the leg when she kicked out at him.
The suspect fled but was arrested nearby. He was held on $1 million bond. It's not clear if he has an attorney.