Harrell struggled during most of the exhibition season as the Packers sought to find a solid backup for Aaron Rodgers, who threw only two passes Thursday.
Harrell completed 13-of-15 throws without an interception and delivered touchdown passes of 17 yards to Alex Green and 12 yards to Jarrett Boykin.
Green Bay closed out the summer with a 2-2 record and will host San Francisco in one of the top attractions on the season-opening weekend.
Brady Quinn went 6-of-12 for 83 yards and an interception for the Chiefs, who spent most of the game working on their running attack. Kansas City had 44 rushes and 21 passes.
The Chiefs (1-3) will host Atlanta in their opener.