Brent served five months in jail for intoxication manslaughter last year.
The team placed Brent on the reserved/retired list. The retirement is Brent's second in the last two years.
Brent, 27, attempted a comeback after his first retirement, which followed five months of jail time for intoxication manslaughter stemming from the 2012 death of Cowboys linebacker Jerry Brown Jr.
Brent only appeared in one game last season, recording three tackles. In 2012, he appeared in 12 games and started five for Dallas, tallying 13 tackles, 1.5 sacks and nine assists on tackles.
His first retirement was in July 2013 ahead of his intoxication manslaughter trial the following January, but after serving five months in jail he returned to the Cowboys last September.
Cowboys coach Jason Garrett said that Brent has shifted his focus to his life away from football.
- Stanley Kay