Singleton attended Irvington High School. As a senior linebacker, he received second-team All-state, SuperPrepAll-American, All-area and All-county honors. He also played in the New Jersey North-South All-Star game.
He accepted a football scholarship from Temple University. As a freshman, he appeared in 8 games, starting 6 at strongside linebacker, while recording 31 tackles (one for loss) and 1.5 sacks. He missed the final three games with a fractured right arm.
As a sophomore, he was named the regular starter at strongside linebacker, tallying 74 tackles (second on the team), one sack, 5 passes defensed, 5 forced fumbles (school record) and one blocked punt.
As a junior, he was named the starter at middle linebacker, registering 151 tackles and becoming only the fourth player in school history to surpass 150 tackles in a season. He also added one sack, one pass defensed and one fumble recovery
As a senior, he was a defensive captain at middle linebacker, posting 134 tackles (led the team), one interception, 5 passes defensed and 2 forced fumbles.
He finished his college career as the school's third all-time leading tackler (390), while starting 39 out of 41 games. He also had 5 sacks, one interception, 11 passes defensed, 7 forced fumbles and one fumble recovery.
In 1999, he was a reserve behind Shelton Quarles, making 26 tackles, one interception, 2 passes defensed and 15 special teams tackles. He had one tackle in the Divisional Playoff Game win against the Washington Redskins, before fracturing his left ankle in the fourth quarter, forcing him to miss the NFC Championship Game against the St. Louis Rams.
In 2000, he registered 32 tackles, one pass defensed, 11 special teams tackles (tied for fifth on the team), one forced fumble and one blocked punt. He suffered a knee injury in the 13th game against the Dallas Cowboys, which forced him to miss the final 3 contests of the regular season.
In 2001, he posted 32 tackles, one sack, 2 passes defensed and 11 special teams tackles (sixth on the team).
In 2002, he was named the starter at strongside linebacker after Quarles was moved to the middle linebacker. He finished with 89 tackles, one interception, 3 passed defensed and 3 special teams tackles. He also contributed to the team having the league's top ranking defense and winning Super Bowl XXXVII.
Dallas Cowboys
On March 13, 2003, he signed with the Dallas Cowboys as a free agent to take over the starting strongside linebacker position, that was previously handled by the departed Kevin Hardy.[2] He recorded 57 tackles (sixth on the team), 7 quarterback pressures, 5 passes defensed, 3 special teams tackles, 2 interceptions (tied for second on the team) and one returned for a touchdown. He also helped the team have the league's top ranking defense.
In 2004, he had 57 tackles (sixth on the team), one quarterback pressure, one pass defensed, 3 special teams tackles, one forced fumble and one fumble recovery. He missed the last 3 games after being placed on the injured reserve list with an abdomen injury on December 23.[3] He was replaced with Scott Shanle.
In 2005, the team switched to a 3-4 defense, but he was still able the remain the starter at the left outside linebacker position, until suffering a broken clavicle against the Arizona Cardinals during the week 8 and being placed on the injured reserve list on November 1.[4] He appeared in 7 games, making 19 tackles, 3 quarterback pressures, 3 passes defensed, one interception and 4 special teams tackles. He was replaced with Scott Fujita.
In 2006, he lost his starting job after Greg Ellis was converted from a defensive end into an outside linebacker, but was able to start 6 games after Ellis was lost for the season with an Achilles injury. He finished with 22 tackles, one sack, one pass defensed, 8 special teams tackles (seventh on the team) and one forced fumble. He wasn't re-signed at the end of the season.