He was selected by Indianapolis in the first round of the 2003 NFL draft and he was a member of their Super Bowl XLI championship team against the Chicago Bears.

As a junior, Clark was named his team's most valuable player and a first-team all-conference and honorable mention all-state selection after recording 140 tackles.

He was team captain and MVP again as a senior, recording 160 tackles, and earned first-team all-conference and second-team all-state honors.

Prior to the 2001 season, the Iowa coaching staff decided to move Clark to the tight end position.

He also played special teams, recovering an on-side kick to clinch a win against Penn State and recording five tackles on the year.

After being granted a scholarship for 2002, Clark started all 13 games as he helped lead Iowa to its first undefeated conference season in 80 years.

With the Hawkeyes trailing, 28–24, Clark caught a seven-yard pass on fourth and goal from quarterback Brad Banks to give Iowa a 31–28 win.

[3] He won the Kenny Yana Award at the end of the 2002 season as well, as he helped lead Iowa to the Big Ten title and an 11–2 record.

[6] When drafted, the Colts called Clark a "perfect fit" for their system, eventually replacing Marcus Pollard and Ken Dilger at the position.

On December 28, 2008, Clark broke the Colts' franchise record, held by Hall of Famer John Mackey, for yards in a season by a tight end (848).

[11] Clark's surgically repaired wrist would again hinder his production in the 2011 regular season, limiting him to 34 receptions for 357 yards and two touchdowns in only 11 games.

[18] Clark guest starred in the CBS hit show Criminal Minds as San Diego Police officer Austin Kent in the episode "The Stranger", fulfilling an acting dream".