It's the second time Brent has retired since his conviction for intoxication manslaughter in the crash that killed teammate Jerry Brown in 2012. The Cowboys placed Brent on the reserve/retired list Friday.
"It is with careful consideration, much thought and reflection that today I announce my retirement from the NFL," Brent said in a statement. "I have not taken this decision lightly, as my time in the NFL and as a member of the Dallas Cowboys has been the opportunity of a lifetime. Two of the greatest institutions in sports are the NFL and the Dallas Cowboys and I am humbled, honored and blessed to have been a part of both.
"I have made the decision that Football isn't as much of a priority in my life as other things at this time."
Brent thanked Cowboys owner Jerry Jones, executive vice president Stephen Jones, coach Jason Garrett, teammates and Dallas fans in the statement.
"I visited with Josh yesterday, and he decided to retire from the NFL at this point, and he's going to focus on continuing to get his life back in order," Garrett said Friday. "I admire Josh in a lot of ways for coming back from a really significant situation in his life. It's not easy. He's worked very hard to find some normalcy in his life at this point, and I think he wants to focus on that right now. We wish him nothing but the best, and we're here to support him in any way we can."
Brent, 27, returned to football briefly last year after serving a 10-game suspension. He played in one game in his first action in almost exactly two years.
Brent had been participating in the Cowboys' offseason program since it began last month. Garrett said Brent met with Jerry Jones earlier in the week to discuss his future.
By placing him on the reserve/retired list, the Cowboys maintain his rights if he chooses to return to football.
"I was a little surprised by it," defensive tackle Nick Hayden said, "but he's got to do what's right for him, so I wish him well and just hope the best for him."
Brent retired before training camp in 2013 while awaiting trial in the case. A 10-year prison term imposed after his conviction in early 2014 was suspended, and he ended up serving about six months in jail.
Brent also had a drunken-driving conviction in Illinois, where he played college football.
Information from ESPN Cowboys reporter Todd Archer and The Associated Press was used in this report.