Ryan Ellis and Roman Josi each had two assists for Nashville (14-5-1), which ended a three-game losing streak. Pekka Rinne made 25 saves.
"It was nice, especially to get a win here at home after a couple of tough losses on the road here," Jarnkrok said.
WATCH: [All Kings vs. Predators highlights]
Anze Kopitar had a goal and an assist, and Cal Petersen made 38 saves for Los Angeles (6-12-1), which has lost four of its past five games.
Jarnkrok gave the Predators a 4-3 lead at 11:54 of the third period while shorthanded to complete the hat trick. He led the rush and scored his sixth goal of the season on a shot from the top of the left face-off circle.
"He's an important player in here, whether it's offensively or defensively," Ellis said of Jarnkrok. "You put him out on the power play and he showed what he can do. He got us going when we needed it, and we got some big goals from him."