Girard was appointed last week following the departure of Rudi Garcia to Roma and he inherits a side that missed out on Europe by a point after finishing sixth, just two years after being crowned Ligue 1 champions.
Former France midfielder Girard arrived at the Grand Stade Lille Metropole following four years with Montpellier, where he led them to a surprise title triumph in the 2011/12 season.
Now the 59-year-old takes charge at Lille looking to build for the future with young talent.
He told the club's official website: "As stated by the president, a sports cycle has ended.
"It will be apparent the last five seasons have been really extraordinary for LOSC, at national and European level.
"I just want to say to those who love the club - do not worry, we have a good team again this season.
"It will probably be a little less mature than in the past, but that is a direction that LOSC will use, to build on the young shoots of the training centre.
"Of course, we will need the support of our fans to push us to excel in this magnificent stadium. "