Graswald admits that she pulled the plug to the kayak, knew the drain plug was out, and the ring was not on the paddle of Vincent Viafore's kayak in April 2015.
She also admitted to knowing that the weather would be dangerous, knew he was drinking, and also that he was not wearing gear and that caused a risk of death that she failed to perceive.
A Cornwall police officer had testified that she appeared calm and emotionless after she was rescued.
Graswald has earlier denied murder and manslaughter charges and her lawyer has argued that Viafore died accidentally after having had a few beers and falling into the cold water.
The drowning death was ruled a homicide by a medical examiner who wrote in an autopsy report obtained by The New York Times that Viafore's death was the result of a "kayak drain plug intentionally removed by other."
Defense attorney Richard Portale told the newspaper the medical examiner's ruling was ill-informed and lacked medical evidence.
Graswald told ABC News in an interview broadcast in November that she loved Viafore and wouldn't have done anything to kill him. She said she's a good person, not a killer.
Graswald faces one to four years behind bars when she is sentenced on Nov. 1. Portale said with the time she's already been in custody she would likely be out by late December.
Hoovler said the guilty plea will make Graswald, who has legal permanent U.S. residency, liable to be deported. Portale said if the federal government filed to have her deported, there would be a court proceeding to contest it.
The Associated Press contributed to this report
Report a typo to the ABC13 staff