Harris led the No. 15 Tigers (4-1, 0-1 SEC) to seven touchdowns in seven possessions after replacing struggling starter Anthony Jennings in the second quarter of Saturday's 63-7 win over New Mexico State.
Harris also nearly led LSU to a comeback victory against Mississippi State the previous Saturday, directing a pair of touchdown drives in the game's final four minutes.
"I think he deserved the opportunity to take snaps," Miles said at his Monday news conference. "I don't think it was a difficult decision."
Harris went 11-for-14 for 178 yards and three touchdowns and ran for two more scores in roughly two quarters of work against New Mexico State, with the Tigers rolling up 429 yards of total offense in that time.
Meanwhile, in seven possessions, Jennings was responsible for three turnovers (two interceptions and a fumble) and the Tigers' offense went three-and-out twice before Miles finally removed him from the game.
Jennings has started LSU's past six games, including wins over Iowa and Wisconsin, and the Tigers are 5-1 in his starts. However, LSU's offense was unproductive against Mississippi State before Harris entered the game in the 34-29 loss, and many fans in Tiger Stadium began to boo each time Jennings jogged onto the field for a new possession once things went south against NMSU.
Miles, after announcing the switch, still attempted to defend the sophomore quarterback.
"It stands to reason that [Harris] would get the first snaps in the next game, but we're going to need both quarterbacks," Miles said. "Anthony Jennings is a fine young man who busted his behind to improve and certainly is going to continue to compete. I think what has to happen, too, is you have to realize that these are young guys that are not perfect and there's an opportunity for him to improve."
Miles said after the NMSU game that he was not ready to anoint Harris as LSU's new starter, but said Monday that he felt the freshman needed to know that the job is his against Auburn.
"He needs to know, and that's not going to be something that I'm going to hide from him," Miles said. "I don't want him to have to field questions."
Auburn (4-0, 1-0) is 11-0 at home since Gus Malzahn became head coach last season.
Jennings has made two starts at neutral sites, but neither he nor Harris has started a game in an opponent's home stadium. Harris played one series in LSU's game against Wisconsin in Houston, and communication appeared to be an issue as the Tigers went three-and-out.
"Our guys have been through hostile environments before," Miles said. "The noise is, in my opinion, a distraction, and the game is certainly the piece that needs to be focused on. I think our guys will get that."