The plea was in exchange for a count of aiding and abetting second-degree murder being dismissed, according to the Associated Press.
The plea came as jury selection was about to start on Monday. Kueng is the second officer to plead guilty to the charge levelled by the state following former officer Thomas Lane pleading guilty to the same charge.
Fellow former officer Tou Thao is set to go to trial this week.
Kueng, Lane, and Thao have already been convicted on federal charges of willfully violating the civil rights of Mr Floyd, a 46-year-old Black man.
Lane was sentenced to two and a half years, Kueng to three years, and Thao to three and a half years in the federal case.
Some members of the Floyd family and a number of activists have argued that those sentences were too lenient.
The 46-year-old father was killed on 25 May 2020 when then-officer Derek Chauvin, a white man, held down a handcuffed Mr Floyd with a knee on his neck for nine minutes despite him saying that he was unable to breathe several times.
A video of the moment filmed by a witness served as crucial evidence in the trial of Chauvin and was widely shared on social media and in news outlets, prompting nationwide and international protests against police brutality and demonstrations for racial justice.
Lane and Kueng both took part in restraining Mr Floyd, with Kueng kneeling on his back and Lane holding down his legs. Thao stopped witnesses from taking action.
Kueng’s plea indicated that a sentence could be three and a half years, but a judge will make the final ruling. Following his state plea, Lane was sentenced to three years – the state sentence will be served concurrently with the federal sentence.
On the state level, Chauvin was sentenced for murder and manslaughter to 22,5 years in April of last year. On the federal level, Chauvin has also pled guilty to violating Mr Floyd’s civil rights. He was sentenced to 21 years in that case and for a separate case concerning a 14-year-old boy.
He’s serving both sentences simultaneously at the Federal Correctional Institution in Tucson, Arizona.
Lane is white, Kueng is Black, and Thao is Hmong American – all of them were convicted on their federal charges in February of this year following a trial that lasted months and outlined their training and the culture within the police department, the Associated Press noted.
They were convicted of denying Mr Floyd’s right to medical care, with Thao and Kueng also being convicted of not intervening to stop Chauvin from killing him.
Following their sentences on the federal level, there were questions surrounding if Thao and Kueng would go to trial. Legal experts said they would probably try to get a plea deal on the state level that wouldn’t go beyond their federal sentences and that would let them serve both simultaneously.
On second-degree unintentional manslaughter for an individual without a previous criminal record, such as Kueng, the state sentencing guidelines suggest a sentence between three and a half and four years, with the presumptive sentence being four years, according to the news agency.
The presumptive sentence for aiding and abetting second-degree murder is 12.5 years.