ESPN Dallas' Calvin Watkins first reported the news.
Okoye, born in Nigeria, was drafted 10th overall by the Houston Texans when he was just 19 years old. The 6-foot-2, 292-pound tackle became the youngest player to start an NFL game since 1967.
Now 26, Okoye spent four seasons in Houston and two in Chicago. In 2013, he was out of football reportedly due to an undisclosed medical issue.
While he's still young, Okoye never lived up to his draft status in Houston, combining for just 5.5 sacks in the three campaigns after his rookie season. The Texans released him in 2011.
The Cowboys need as much help as they can get on the defensive side of the ball, so taking a flyer on Okoye makes sense. The defensive tackle is familiar with current Cowboys defensive coordinator Rod Marinelli from their time together in Chicago.