[6] At cornerback, McKelvin was credited with 30 tackles, including 26 solo stops, one sack, a fumble recovery and five pass breakups.

McKelvin was credited with one tackle for loss during the season, had two forced fumbles, two quarterback hurries and seven pass breakups.

[13] The following week on Sunday on the road against the Kansas City Chiefs, McKelvin intercepted Tyler Thigpen twice, returning one for a 64-yard touchdown.

[16] After Jabari Greer left via free agency during the 2009 offseason, McKelvin was named the starting cornerback opposite Terrence McGee to begin the season.

On September 14, 2009, during the Bills' season opener on Monday Night Football, McKelvin caught a kickoff in his own endzone with Buffalo up 24–19 over the New England Patriots and 2:06 left in the game.

[17][18] As a result, two teenage males vandalized the Hamburg, New York, home of McKelvin spray-painting obscenities as well as the phrase "take a knee" and the winning score of 25–24 in favor of New England on his front lawn.

He made his return on September 12, 2010, in the season opener against the Miami Dolphins and finished the 15–10 loss with three tackles and two pass deflections.

[33] McKelvin finished the season with 39 total tackles, eight pass deflections, and one interception while appearing in all 16 games with six starts.

[34] To begin the season, he was the third cornerback on the depth chart behind Aaron Williams and rookie Stephon Gilmore but continued to handle punt and kick return duties.

[41] He began the season as a starting punt returner and cornerback after Aaron Williams was switched to strong safety.

During the season opener against the New England Patriots, McKelvin finished with a total of six tackles and four pass deflections as the Bills lost 23–21.

[42] On December 1, 2013, he finished with a career-high ten tackles and two pass deflections during a 34–31 overtime loss to the Atlanta Falcons in Toronto.

[44] McKelvin started the 2014 season with a career-high 13 solo tackles and forced a fumble during a 23–20 victory over the Chicago Bears.

[48] He finished the season with 48 combined tackles, eight pass deflections, and a career-high four interceptions in nine starts and ten games.

[52] He finished his first and only season under new head coach Rex Ryan with 32 total tackles, nine pass deflections, and two interceptions.

[54] McKelvin signed with the Philadelphia Eagles on March 8, 2016, reuniting with the defensive coordinator Jim Schwartz, who was with Buffalo in 2014.

[56] He played in 13 games with 12 starts for the Eagles in 2016, recording 43 tackles, 16 passes defensed and two interceptions including one returned 29 yards for a touchdown in Week 14 against the Washington Redskins in a 27–22 loss.