Kiwanuka was selected with the 32nd overall pick of the
2006 NFL draft by the
New York Giants. On July 25, 2006, he signed a five-year $10 million contract with $5 million guaranteed. In his first season, he played
defensive end and played in all 16 regular season games with 9 starts and finished the season with 55 tackles (41 solo), 4 sacks, 2 interceptions and 2 forced fumbles. In 2007, he won the starting strongside
linebacker position after spending the entire offseason learning the new position following a rookie year spent at defensive end. On September 30, 2007, Kiwanuka recorded 7 tackles and 3 sacks in a 16–3 victory over the
Philadelphia Eagles. Kiwanuka's season ended at Detroit on November 18, 2007, when he suffered a fractured left fibula. He had surgery to stabilize his leg and ankle the following morning and was placed on
Injured Reserve, ending his 2007 season. He started all 10 games in which he played and finished the season with 47 tackles (24 solo), 4.5 sacks, 4 passes defensed, 1 forced fumble. Meanwhile, the Giants went on to win the
Super Bowl. In 2008, Kiwanuka entered training camp as the starting strongside linebacker, but returned to defensive end when
Osi Umenyiora suffered a season-ending knee injury during the preseason. On December 14, 2008, Kiwanuka recorded a safety, recorded 5 tackles, and forced a fumble in a loss against the
Dallas Cowboys. He started all 16 games and the NFC Divisional Playoff game at right defensive end and finished the season with 59 tackles (28 solo), 8.0 sacks, 13 tackles for loss, 2 passes defensed, 2 forced fumbles and 2 fumble recoveries. Through the 2008 season, Kiwanuka had played in 42 regular season games with 35 starts – 25 starts at defensive end and 10 starts at strongside linebacker. He has also started 2 postseason games at defensive end. In 3 seasons, he has 161 tackles (93 solo), 16.5 sacks, 2 interceptions and 5 forced fumbles. Kiwanuka was placed on injured reserve on October 28, 2010, due to a herniated disc. On April 27, 2012, the Giants extended Kiwanuka's contract, giving him $16.5 million over 3 years with $10.5 million guaranteed. While playing with the Giants, Kiwanuka was a resident of
Hoboken, New Jersey. On February 21, 2013, the Giants and Kiwanuka agreed on a restructured contract. The restructured deal, converted $1.5 million of Kiwanuka's 2013 guaranteed base salary into a signing bonus. The new deal saved the Giants approximately $1 million towards their 2013 salary cap, but slightly increased his cap number in both 2014 and 2015. On February 24, 2015, Kiwanuka was released. ==NFL career statistics==