Coffman was born in Lee's Summit, Missouri and played high school football at Raymore–Peculiar High School in nearby Peculiar. Coffman had a great high school career receiving passes from his younger brother Carson. He earned first-team all-state honors three times and was a two-time first-team all-district and all-conference pick. During his senior year in 2004, he was named conference player of the year and won the Simone Award after catching 41 passes for 886 yards and 16 touchdowns. He was also a standout basketball player, earning first-team all-conference honors in 2003 and 2004.
Coffman attended the University of Missouri, where he played for coach Gary Pinkel's Missouri Tigers football team from 2005 to 2008. During his freshman year in 2005, he had one of Missouri's best seasons ever for a tight end. He finished the season with 47 receptions for 503 yards and 4 touchdowns, and earned First-Team Freshman All-American honors by Rivals.com. Coffman had an amazing 2006 campaign leading all Big 12 tight ends with 58 catches for 638 yards and nine touchdowns, all of these were also Missouri records for tight ends. Because of his great season he was awarded First-Team All-Big 12 and was a finalist for the John Mackey Award. Although not matching his 2006 season he still had a great 2007 season finishing with 52 receptions for 531 yards and 7 touchdowns. Because of his play he was a second-team All-Big 12 selection and again was a finalist for the John Mackey Award. Entering the 2008 season he became Missouri's all-time leader in receiving touchdowns with 20, third in receptions with 156 and seventh in receiving yards with 1,664.
As a senior in 2008, he won the John Mackey Award, given annually to the nation's best tight end. He became the first Missouri player to win the award. He had 90 receptions for 987 receiving yards and 10 touchdowns.
Coffman was drafted by the Cincinnati Bengals in the third round of the 2009 NFL draft. On December 9, 2009, Coffman was placed on season-ending injured reserve due to a left ankle injury. He finished his rookie season being inactive for all 12 games he was on the active roster.
On September 4, 2010, the Bengals waived Coffman. They re-signed him to their practice squad the next day. A year later, he was waived on September 4, 2011, and signed to the Bengals' practice squad the following day. He was not signed to the Bengals reserve list following the 2011 season after his practice squad contract expired.
On February 21, 2012, the Tampa Bay Buccaneers signed Coffman as a free agent. On August 6, 2012, Coffman was waived.
On August 11, 2012, the Atlanta Falcons signed Coffman. Two weeks later, on August 25, he was waived. Coffman was signed to the Falcons practice squad on September 2, 2012. Coffman was signed to the Falcons 53-man roster on November 13, 2012.