He faces up to 20 years in prison when he is sentenced on Oct. 1.
Thompson admits in court papers that he stabbed Wright in the neck and abdomen with a knife in the early morning hours of July 4, 2012.
Thompson had gone to the Payson house party after his 15-year-old cousin called him, asking for help with an "altercation," according to prosecutors.
But witnesses testified during Thompson's preliminary hearing in April that the teen was upset after he had been told several times to leave the party, since he was underage and alcohol was being served.
"He kept trying to drink," testified Amanda Calton, a partygoer. "He was going and stealing beer, and he was being very disrespectful and rude. … He got kicked out of the party a few times, because he wasn't welcome there. He wasn't old enough."
Partygoers testified that Wright was trying to be "the peacekeeper" during the party at his home, but as the party began to wind down, the teen began yelling threats from across the street, saying his cousin was coming to kill them.
Soon after, witnesses testified that a car came to a screeching halt in front of the house, and Thompson exited his car.
According to a probable cause statement, Thompson told police that a man rushed toward him as he exited his car, so he grabbed a knife and began "swinging at the male with his fists," the document states.
Thompson told police that he didn't know whether he had cut Wright in the scuffle, but witnesses said he didn't stick around to find out.
Thompson and his younger cousin got into his car and drove to Spanish Fork, prosecutors said. Along the way, Thompson threw the knife out the car window and stripped off a layer of clothes he was wearing another shirt and pants and put the top layer in a Dumpster, according to court documents.
In Spanish Fork, the teen said, Thompson "freaked out" and said, "I hope I didn't kill him."