[4] Stewart was selected as the Huntsville Times Super All-Metro Most Valuable Player as a senior and was named finalist for the 5A Back of the Year Award.

[8] Throughout training camp, he competed for a roster spot and a job as a backup safety against David Roach, Craig Dahl, James Butler, and Kevin Payne.

[11] On December 12, 2010, Stewart collected two solo tackles and recorded his first career sack on quarterback Drew Brees during the Rams' 31–13 loss at the New Orleans Saints.

[12] Stewart entered training camp competing in a competition to name a starting free safety after it was left vacant by the departure of Oshiomogho Atogwe.

[13][14] Defensive coordinator Ken Flajole named Craig Dahl as the starting free safety, alongside Quintin Mikell, with Stewart as his backup to begin the regular season.

In Week 8, Stewart recorded seven combined tackles, two pass deflections, and returned an interception by Drew Brees for a 27-yard touchdown during a 31–21 win against the New Orleans Saints.

On November 27, 2011, he made seven combined tackles and a sack before leaving the Rams' 23–20 loss to the Arizona Cardinals in the fourth quarter after sustaining a concussion.

[19] Stewart was slated to retain his starting role and competed against Craig Dahl, Matt Daniels, and Rodney McLeod throughout training camp.

[20] Stewart suffered a hamstring injury during training camp and missed the majority of the preseason and the first two games of the regular season.

[21] Head coach Jeff Fisher opted to keep Craig Dahl at free safety and named Stewart the backup once he returned in Week 3.

[12] On March 21, 2013, the St. Louis Rams signed Stewart to a one-year, $1.3 million restricted free agent tender with a right of first refusal clause in his contract.

[8][23] He entered training camp slated as the starting strong safety after Craig Dahl and Quintin Mikell departed in free agency.

[25] In Week 5, he started at free safety and recorded a season-high six combined tackles in the Rams' 34–20 win over the Jacksonville Jaguars.

Stewart finished the 2013 season with 36 combined tackles (30 solo), five pass deflections, and a forced fumble in 13 games and six starts.

[26] Stewart was the favorite to earn the starting job at free safety entering camp and competed against Jeromy Miles and Terrence Brooks.

[31] The following week, he made two solo tackles as the Ravens lost 35–31 to the eventual Super Bowl XLIX Champions the New England Patriots.

On March 12, 2015, Stewart attended a visit with the Denver Broncos and received a contract offer after he met with team representatives.

Throughout training camp, Stewart competed against David Bruton for the job as the starting free safety after it was left vacant by the departure of Rahim Moore.

[38] Stewart was an integral part of the Denver Broncos' successful 2015 season and helped them finish first in the AFC West with a 12-4 record.

On February 7, 2016, Stewart recorded three combined tackles, two pass deflections, a forced fumble, and sacked quarterback Cam Newton in the Broncos' 24–10 victory against the Carolina Panthers in Super Bowl 50.

[40][41] The Broncos retained all five members of the "No Fly Zone" as their key starters entering training camp and to start the regular season.