Man Utd sell young pair De Laet, James to Leicester
De Laet, 23, and James, 20, join the Foxes for an undisclosed fee, on three-year deals running until June 2015.
Leicester manager Nigel Pearson revealed the club had been monitoring the pair for "some time" and said he was "very pleased" to wrap up the deal.
"Both are hungry, young players with winning mentalities, experience of Championship football and a desire to be successful," he said. "They will add considerable quality to the squad."