He played college football for the Western Michigan Broncos and was selected by Green Bay in the second round of the 2006 NFL draft.

As of 2025, he is a recurring guest football analyst on the Fox Sports 1 (FS1) programs First Things First and Breakfast Ball.

[1] Jennings finished seventh in voting for Mr. Basketball of Michigan in 2000–01[2] and scored a school record 50 points in a losing effort against Benton Harbor as a senior.

[1] In track & field, Jennings was one of the state's top performers in the long jump event.

[9] Jennings was named the starting wide receiver, along with Donald Driver, which put Robert Ferguson in the slot, for his first professional regular-season game Green Bay Packers by head coach Mike McCarthy on September 2, 2006.

Jennings was voted NFL Rookie of the Week for games played September 24–25, 2006, the only time he received this honor.

On September 23, 2007, Jennings caught a game-winning 57-yard TD pass from Favre with less than two minutes to play to help beat the San Diego Chargers 31–24 at Lambeau Field and improve the team's record to 3–0 in 2007.

A week later on September 30, 2007, during a 23–16 victory over the Minnesota Vikings, Jennings caught a 16-yard pass from Favre that opened the scoring ten minutes into the first quarter, and broke the all-time touchdown pass record Favre had shared with Dan Marino.

Then the following week, he caught the game-winning touchdown pass that went for 60 yards to beat the Chiefs in Kansas City.

Against the Cowboys on November 29, 2007, in a game broadcast on the NFL Network, Jennings hauled in the first ever touchdown pass by quarterback Aaron Rodgers.

[12] Jennings caught a game-winning pass on September 13, 2009, on a 3rd and two play, where the Packers ran a play action fake and rolled Aaron Rodgers out to the left, who then threw a 50-yard pass to Jennings to defeat the Chicago Bears in the season opener.

[13] In the Packers 2009 Wild Card game against the Arizona Cardinals, Jennings had 8 receptions for 130 yards, scoring 1 touchdown.

[14] In Super Bowl XLV, on February 6, 2011, Jennings caught four passes for 64 yards and scored two touchdowns in the Packers' 31–25 victory over the Pittsburgh Steelers.

[29] On May 5, 2010, Jennings made an appearance on the CBS prime time hit show Criminal Minds.

The entire charity organization raises money through organizational events, donations, and fund raisers.

[citation needed] Jennings is also a part-time analyst on FS1's First Things First and Breakfast Ball, and formerly on The Carton Show.