Financial terms of the four-year contract (which includes a team option for 2015) were not disclosed.
"We are very happy that Corey’s contract is done. It’s time to go to work," Chargers general manager A.J. Smith said.
The 6-foot-2, 298-pound Liuget turned pro after a breakout junior season at the University of Illinois, recording 63 tackles and 4.5 quarterbacks sacks and earning second-team All-Big Ten honors in his first season as a full-time starter.
One of the more versatile defensive linemen in this year's draft class, Liuget has the ability to play anywhere along the defensive line. San Diego selected Liuget with the 18th overall pick to eventually supplant Jacques Cesaire as the starter opposite Luis Castillo.
The 30-year-old Cesaire is signed through the 2012 season, but Liuget could earn a starting role in 2011.
With Liuget agreeing to terms, New England Patriots offensive tackle Nate Solder, New York Giants cornerback Prince Amukamara, and Kansas City Chiefs third-round linebacker Justin Houston are the only draft picks without contracts.