Superior Court Judge John Cheroske sentenced Fisher to 25 years to life in prison.
Fisher pleaded guilty last month to the first-degree murder of Dae'von Bailey.
The child's body was found brutally beaten July 23 at a home in the 800 block of East 87th Place.
The boy's mother, who is Fisher's ex-girlfriend, had left her son in Fisher's care.
Prosecutors said Fisher became upset with the child and beat him for more than half an hour.
Fisher fled the crime scene.
He was arrested one month later in North Las Vegas.
In exchange for his guilty plea, the District Attorney's Office dismissed a felony count of assault on a child causing death.
D.A. officials say the felony count would not have added any additional time to the sentence.