Alleva said LSU already planned to offer Miles an enhanced contract after this season, but decided to close the deal now to snuff out speculation that Miles could be lured elsewhere.
"Speculation about other job opportunities accelerated our process a little," Alleva said. "I think we have accomplished the important step of securing Les Miles as our head coach for the long-term good of the program."
In the short-term, Miles has given his team two weeks off.
The Tigers will find out their bowl destination Sunday with the Capital One Bowl, the Cotton Bowl and the Chick-fil-A Bowl being the leaders. LSU will begin bowl practice after fall exams end Dec. 8.
"We look forward to playing in a quality bowl game," Miles said. "We should add two starters (linebacker Kwon Alexander and guard Josh Williford). We should be healthy. I think we'll fill the bowl arena. There is speculation as to which bowl. I know LSU will be in attendance and that will be enough."
LSU's 21-17 loss to Alabama, for all practical purposes, ended its opportunity to repeat as SEC champion. With a loss at Florida, the Tigers finished with a 10-2 record. LSU posted that mark even though six projected starters missed all or most of the season.
"I would never take 10-2 as a final" record, Miles said. "But, as this year played out, I think this team improved. Three games into (the season), the team changed numbers. We had key players not there. Guys stepped in and played big. This team fought like hell and fought adversity."
Bryan Lazare contributed to this story from Baton Rouge, La.