[6] One of the most memorable moments of his career was against archrival Michigan when he returned a Chad Henne fumble for a touchdown in front of a roaring crowd at Spartan Stadium.

On March 18, 2006, he participated at Michigan State's pro day, but opted to stand on his combine numbers and only ran positional drills.

At the conclusion of the pre-draft process, Peko was projected to be a fifth or sixth round pick by NFL draft experts and scouts.

[16] Head coach Marvin Lewis named Peko a backup defensive tackle to start the regular season in 2006, behind Sam Adams and John Thornton.

[17] He made his professional regular season debut in the Cincinnati Bengals' season-opener at the Kansas City Chiefs and recorded two solo tackles in their 23–10 victory.

[18] On October 29, 2006, Peko collected a season-high seven combined tackles and made his first career sack during a 29–27 loss against the Atlanta Falcons in Week 8.

[19] Throughout training camp in 2007, Peko competed to be a starting defensive tackle against Michael Myers, John Thornton, Kenderick Allen, and Matt Toeaina.

[24] Head coach Marvin Lewis named Peko a starting defensive tackle to begin the 2007 NFL season.

[26] On December 15, 2007, he collected a season-high nine combined tackles and was credited with half a sack in the Bengals' 20–13 loss at the San Francisco 49ers in Week 15.

[33] Peko started in all 16 games in 2008 and recorded a career-high 67 combined tackles (29 solo), two passes defended, and was credited with half a sack.

[36] On November 29, 2009, Peko made one tackle before exiting in the third quarter of the Bengals' 16–7 win against the Cleveland Browns in Week 12 due to a knee injury.

[41] On January 9, 2010, Peko started in his first career playoff game and recorded four combined tackles in their 24–14 loss to the New York Jets in the AFC Wild Card Round.

[42] Head coach Marvin Lewis named Peko the starting nose tackle in 2010, alongside defensive ends Antwan Odom and Robert Geathers.

[43] On November 25, 2010, Peko collected a season-high seven combined tackles and broke up a pass in the Bengals' 26–10 loss at the New York Jets in Week 12.

[44] Peko started in all 16 games in 2010 and recorded 42 combined tackles (24 solo), one pass deflection, and was credited with half a sack.

[49] On January 7, 2012, Peko recorded four solo tackles in the Bengals' 31–10 loss at the Houston Texans in the AFC Wild Card Round.

[60] On January 5, 2014, Peko recorded two solo tackles as the Bengals lost 27–10 to the San Diego Chargers in the AFC Wild Card Round.

[79][14] Head coach Vance Joseph named Peko the starting nose tackle to begin the regular season, alongside defensive ends Jared Crick and Derek Wolfe.

[80] On November 26, 2017, Peko made six combined tackles before exiting in the fourth quarter of the Broncos' 21–14 loss at the Oakland Raiders due to a sprained MCL.