Okoye, who was out of football last season due to an undisclosed medical issue, is reunited with Cowboys defensive coordinator Rod Marinelli, who coached Okoye with the Chicago Bears (2011-2012).
"We like a lot of things about him," coach Jason Garrett said. "He was a high draft pick a few years ago, a really young player coming out of school, and he has a lot of talent. Rod was around him in Chicago, we know him well, he's had an intimate-type relationship. So we think that's a real positive thing.
"He's had some health issues the last year or so where he lost a lot of weight. He's gained his weight back and we're waiting on some medical things. We feel like he has a chance to be a contributor on that defensive line."
Okoye will turn 27 on June 10. He was 19 when the Houston Texans selected him 10th overall in the 2007 draft.
Born in Anambra, Nigeria, Okoye was 16 when he played in his first game for Louisville in 2003.
Information from Calvin Watkins of ESPNDallas was used in this report.