Buffalo Bills

DiGiorgio was signed by the Bills as an undrafted free agent in 2006. That year, he was the only undrafted free agent to make the Bills' 53-man roster. He overcame a lot of adversity, and added depth to a (during the time) weak defense.^[1] As a rookie in 2006, DiGiorgio played in 12 games and made eight tackles. But when London Fletcher departed for Washington after the season, it gave DiGiorgio a chance to compete for the starting job.

DiGiorgio had a big year for the Bills in 2007. He played in all 16 games—the final 13 as a starter at middle linebacker—and was second on the team with 113 tackles. John took full advantage of Paul Posluszny's injury, and filled in as the middle linebacker in the 2007 season. As John filled in for the injured starting linebacker he did an exceptional job. His "blue-collar" work-ethics made him the 2007 Buffalo fan favorite. With Buffalo being a predominate blue-collared environment the fans took notice of John being a natural underdog in the NFL with a great work-ethic. The combination of hard-work and Buffalo natives recognizing his background, adversities, and doing an exceptional job as the backup MLB sparked the Buffalo fans support. He also had two fumble recoveries and an interception. The Bills were in the playoff hunt late in the season, but they lost their final three games to finish with a 7–9 record.

Among DiGiorgio's highlights was his sack of New England Patriots' quarterback Tom Brady in Week 3 for his first career sack. He also intercepted a pass from Tony Romo in a 25–24 loss to the Dallas Cowboys. However, the following season, DiGiorgio appeared in six games primarily on special teams before tearing a ligament in his right knee while blocking on a punt return in the second quarter of a 23–14 win over San Diego in Week 7.

He was waived by the Buffalo Bills on July 25, 2009, for failing his physical after having season-ending surgery to repair bone damage in his right knee.^[2]

He retired on July 25, 2010.