Lissemore, who signed a three-year extension worth $7.17 million and included $3.17 million in guaranteed money last September, was not viewed as a good fit in the Cowboys' new 4-3 scheme.
The Chargers use the 3-4 scheme Lissemore played in his first three seasons. A seventh-round pick in 2010, Lissemore started six of the 28 games in which he played with 85 tackles and 3.5 sacks.
He suffered a concussion in the preseason finale versus Houston.
The trade opens up a spot on the Cowboys' 53-man roster, which could be filled Sunday with a waiver-wire pickup.
The Cowboys will get to see Lissemore in person when they play at San Diego on Sept. 29.