Harris beat out sophomore Anthony Jennings in a prolonged quarterback battle. He will become the first true freshman quarterback to start for LSU since Jordan Jefferson in 2008.
Over four games this season, Harris has passed for 394 yards and six touchdowns against one interception while adding 108 yards and three touchdowns on the ground. In Saturday's 63-7 win over New Mexico State, Harris completed 11 of his 14 pass attempts for 178 yards and three touchdowns.
Jennings, meanwhile, has passed for 732 yards and five touchdowns.
"It stands to reason [Harris] will get the first snaps in the game, but we'll need both quarterbacks," Miles said, according to AL.com. "Anthony Jennings is a fine young man busting his behind, proven and is certainly going to continue to compete."
Harris, who enrolled at LSU last January, was rated the No. 5 dual threat quarterback in the class of 2014 by the recruiting website Rivals.com. Harris also drew scholarship offers from Alabama, Ohio State, Ole Miss and Auburn, among other programs.
"There's some ad-lib to his game that is very, very positive," Miles said. "He's a guy that really is fast and a guy that can really throw the ball, so you put him in a quality position to extend a play, some good things can happen."
LSU, ranked 15th in the latest AP Poll, is 4-1 this season with wins over Wisconsin, Sam Houston State, Louisiana Monroe and New Mexico State and a loss to Mississippi State. Saturday's game at Auburn is its first SEC road contest of the season.
Auburn, ranked 5th, is undefeated with wins over Arkansas, San Jose State, Kansas State and Louisiana Tech. Auburn has not lost at home since the 2012 season.
- Chris Johnson