Tanney broke nearly every school record during his time at Monmouth. His career began in 2007 when he threw for 2,678 yards and 24 TDs. In his sophomore season in 2008, Tanney broke the Monmouth record of single season TD passes with 50. For his junior campaign, Tanney threw for 3,856 yards and 44 TDs which led him to be named the Melberger Award winner as D-III's top player. After redshirting the 2010 season with an injury, he came back in 2011 and threw for a career-high 3,867 yards along with 38 TDs. He won three Midwest Conference Offensive Player of the Year Awards in his college career along with numerous All-American Awards.
On October 29, 2011, in a game against Carroll University, Tanney set the NCAA record for all-time all-division career touchdown passes with 150, surpassing Jimmy Terwilliger's record of 148. Tanney finished his collegiate career with 157 touchdown passes and also holds the D-III record for most passing yards in a career with 14,249.
Tanney signed a contract with the Kansas City Chiefs as an undrafted free agent on June 5, 2012. He was placed on injured reserve with a finger injury on September 1, 2012.
On November 26, 2013, the Cleveland Browns signed Tanney off the Cowboys' practice squad. On May 12, 2014, the Browns released Tanney.
Tanney was signed to the practice squad of the Tennessee Titans on December 16, 2014. He signed a futures contract with the Titans on December 29, 2014. The Titans released Tanney on September 5, 2015.
On December 21, 2015, Tanney was signed off the Colts practice squad by the Tennessee Titans. He made his NFL regular-season debut on January 3, 2016 against the Indianapolis Colts, relieving the injured Zach Mettenberger in the third quarter and going 10-for-14 for 99 yards and throwing his first career touchdown pass, to Dorial Green-Beckham. On September 13, 2016, he was waived by the Titans and was re-signed to their practice squad the next day. On December 27, 2016, he was promoted to the active roster.
On September 2, 2017, Tanney was placed on injured reserve.
