He was born in St. Cloud, Minnesota, however his family moved to Litchfield right after his birth. Carlson graduated from Litchfield High School. As a football player, he was all-state Minnesota in his Senior year. He played in the 2003 U.S. Army All-American Bowl alongside fellow Notre Dame Fighting Irish players Brady Quinn, Ryan Harris, and Tom Zbikowski. As a basketball player, Carlson was voted to the preseason McDonald's All-American list. He led the Litchfield Dragons to three state basketball titles during his freshman, junior and senior years. Carlson was also an all-state tennis player. His dad, John Sr. is the basketball and tennis coach for the Litchfield Dragons.
Carlson played college football at Notre Dame, where he was a two-year starter at tight end. He was named captain in his junior and senior seasons. He recorded 100 receptions, 1,093 receiving yards and 8 total touchdowns in his career. He also lived in St. Edward's Hall, the second-oldest residence hall on campus. His roommate was John Sullivan, current starting center for the Minnesota Vikings.
Carlson was drafted by the Seahawks in the second round (38th overall) of the 2008 NFL Draft. On July 26, he signed a $4.52 million contract including $2.5 million guaranteed.
He scored his first NFL touchdown on a pass from Charlie Frye in week 6 of the 2008 NFL season in a 17-27 loss to Green Bay.
In a season marred by injuries for the Seahawks, particularly at wide receiver, Carlson proved to be a reliable target throughout the season, and led the team in receptions (55) and receiving yards (627) for the 2008 season, a feat not accomplished in franchise history by a rookie since Hall of Fame WR Steve Largent.
Carlson had a notable performance in the Seahawks' 2010 playoffs: in a matchup against the defending Super Bowl champion New Orleans Saints, he had two touchdown catches. In the following divisional matchup against the Chicago Bears, he received a concussion after jumping and being hit in the air and landing on his helmet after receiving a pass near the sideline in snowy Soldier Field.