Allen was born in Dayton, Ohio. He attended Wayne High School in Huber Heights, Ohio, and played high school football for the Wayne Warriors. Was a member of Wayne High School's 1999 Division I State Runner-Up team, along with fellow Ohio State recruit John Hollins. His high school jersey #4 is the only number that has been officially retired by Wayne High School. Allen was named Division I first-team all-Ohio by The Associated Press for his senior season. He was rated as the No. 4 defensive back prospect and the No. 27 overall prospect in the Midwest by SuperPrep, and rated as the No. 53 defensive back prospect in the nation by Rivals100.com.
Allen played in every game in his rookie year on special teams but saw increasing time as a safety in the final weeks of the season. He made his first NFL interception against the Carolina Panthers and his first touchdown in week 6 of the following season against the Miami Dolphins. He started eight games in 2005, playing at both free safety and strong safety due to injuries to Jermaine Phillips and Dexter Jackson. Allen's most noted contribution in his young NFL career occurred against the Green Bay Packers in 2005, when he intercepted Packers quarterback Brett Favre twice in the fourth quarter. Buccaneers starting safety, Dexter Jackson, had been injured midway through the second quarter with a hamstring strain. Allen came into the game as a substitute. Allen was the Buccaneers' special teams captain in 2008. Allen was the first alternate for NFC Special Teams for the 2009 Pro Bowl. He was re-signed to a 1-year $2.35 million contract on February 28, 2009
Pittsburgh Steelers
On March 8, 2010, Allen signed with the Pittsburgh Steelers. On November 9, 2012, Allen was fined $7,875 for a late hit against New York Giants receiver Victor Cruz in Week 9.
On March 27, 2013, Allen signed a one-year, $840,000 contract with the Dallas Cowboys. The deal included a $65,000 signing bonus. He was released on October 8, 2013.
Second stint with Steelers
Allen returned to the Steelers in October 2013. He signed a 1year $1,020,000 contract, then another $1,050,000 contract with the Steelers the following year.
The Will Allen Foundation
The Will Allen Foundation was created in May 2008 to inspire youth to attain their personal best and to be an influence in the lives of families in Dayton, Ohio; Tampa, Florida and Pittsburgh, Pennsylvania. The foundation's main focus is to provide students in the Quest for Real Life Success program with "real" life experiences and expose them to new and rewarding opportunities. Quest allows them to explore their curiosities and gives them the desire to strive and achieve goals outside of the everyday opportunities currently afforded to them. The mission of the Will Allen Foundation is to remove barriers by providing programs and resources for those committed to achieving their personal best, bettering themselves, their families and their communities. The vision of the Will Allen Foundation is to provide a level playing field for all, allowing for each individual to achieve their greatest success.