His first career reception came on a five-yard pass from Hall of Fame quarterback John Elway.
Carswell received the Ed Block Courage Award, after suffering season-ending internal injuries in October 2005,[3] in a car crash in Aurora, Colorado.
He was named Second-team All-State as a sophomore at Temple and also earned All-Conference, All-District and All-County honors during his high school career as a safety, running back and wide receiver.
He spent the first 11 weeks of the season on the practice squad until he was signed to the active roster on November 25.
He made his NFL debut on November 27, 1994, against the Cincinnati Bengals, during the game he played on special teams.
In 1995, Carswell was inactive for seven of the Broncos' first 13 games before making his first career start against the Seattle Seahawks on December 10, when he replaced Shannon Sharpe, who had an eye injury.
In 1996, Carswell played in all 16 of the Broncos regular-season games and started one at tight end in place of Sharpe.
Most of Carswell's playing time during the regular season came on special teams and as the backup tight end on offense.
On January 25, he recorded one receptions for four-yards in a 31–24 win over the Green Bay Packers in Super Bowl XXXII.
In 1998, Carswell played all 16 regular-games, making one start, as the backup tight end and recorded four receptions for 51 yards.
In 2000, Carswell started all 16 regular-season games and set career highs in every receiving category by finishing third on the team with 49 receptions for 495 yards (10.1 avg.)
Nine starts came when the Broncos opened games in a two-tight end set, and his other came at Green Bay on December 28 in place of the inactive Shannon Sharpe.
In 2004, Carswell spent training camp playing at offensive tackle, however he was later switched to tight end.