In his first media conference since being reinstated by commissioner Roger Goodell, Smith told reporters he "got to a point where I was fed up with how I was living my life, and I knew I needed to change."
Smith explained he lost his way at some point: "I wasn't sure what my purpose was. I know football is one of my many purposes that God has put me here (for). ... With God giving me this gift, this talent...it was something I didn't finish."
The Cowboys signed Smith to a one-year deal on April 1, but he still had to apply for reinstatement to the NFL after being suspended for multiple violations of the personal conduct and substance abuse policies.
Roger Goodell reinstated Smith on May 20, officially ending his five-year suspension from the league.
Smith was suspended for one year in November 2015 following an August arrest on charges of hit and run, DUI and vandalism. He was required to apply for reinstatement at the end of the suspension in order to be eligible to play.
NFL spokesman Brian McCarthy told NBC Sports Bay Area's Scott Bair in December 2016 that Smith's application for reinstatement wouldn't be revisited during the season.
The Oakland Raiders, who signed Smith to a two-year deal in April 2016, released him in March 2018 after police issued an arrest warrant for his alleged involvement in a domestic violence incident. He pleaded no contest to two misdemeanor charges in the case and was sentenced to 90 days in jail and three years of probation.
Per Calvin Watkins of the Dallas Morning News, Smith has been sober for nine months as of his signing with the Cowboys.
Smith was a first-round pick by the San Francisco 49ers in 2011. The 30-year-old recorded 47.5 sacks in 59 games over his first five seasons between the 49ers and Raiders.