James Paul Simpkins II, 21, was sentenced Thursday in Genesee County Circuit Court, the Michigan news website Mlive.com reported Friday.
Simpkins was found guilty in January of three counts of first-degree murder, aas well as firearms and sexual assault charges, after a weeklong trial.
Prosecutors said four victims, one of whom was shot but survived, were drinking and smoking marijuana when Simpkins fired a shot in the living room of the house. He then entered a bedroom and shot the victims, including his brother and bother's girlfriend.
The surviving victim, a woman, was sexually assaulted after Simpkins' gun ran out of ammunition. She was choked until she lost consciousness, prosecutors said.
Police identified those killed in the attack as Anthony Simpkins, 21, Bobby Jackson, 36, and Erica Billingsley, 21.