The 44-year-old actor - who now has three sons with wife Viveca Paulin - first became intimate with a woman during his junior year of college, and admitted the experience felt like "the way it was supposed to happen".
He said: "In my mind`s eye, it seemed like the way it was supposed to happen."
However, the `Anchorman` actor explained his mother thought he had lost his virginity during his high school years to a girl who was particularly popular with his male classmates.
Speaking in an interview with Rolling Stone magazine, he added: "She said, `If you slept with this girl, you`d better slap a condom on that pecker of yours`."
Will`s college years in the Delta Tau Delta fraternity at the University of Southern California also saw him strip off on a number of occasions to impress his fellow classmates.
He said: "In college, they had this thing where you`d run naked on fraternity row, and if anyone challenged me, I`d be happy to do it."