Mills played high school football for four years at Assumption High School in Napoleonville, Louisiana. He was a two-time all-district selection for District 8-5A, and was named honorable mention all-state as a senior. He also lettered in basketball for three years and threw the shot puton the track team for three years, while helping lead the track team to regionals as a junior. Considered a three-star recruit by Rivals.com, he was rated the 53rd best offensive tackle in the nation. He accepted a scholarship from Louisiana Tech over offers from Southern Mississippi and Tulane.
College career
In 2009, as a true freshman, Mills, saw action in seven games, starting at left guard in the last five. In 2010, the coaching staff originally planned to redshirt Mills, but a season-ending knee injury to teammate Cudahy Harmon forced Louisiana Tech to pull the redshirt off him. He would go on to play in five games, starting in four at right tackle. In 2011, he started in all 13 games, paving the way for Louisiana Tech's tailbacks to rush for over 1,800 yards. As a senior, he started in all 12 games, and earned first team all-conference honors.
Professional career
Chicago Bears
Mills was drafted by the Chicago Bears in the fifth round, 163rd overall in the 2013 NFL Draft. On May 1, 2013, Mills and sixth-round pick Cornelius Washington were the first players to sign, both signing four-year contracts. After a strong preseason, he won the starting right tackle job. Mills started all sixteen games for the Bears, allowing three sacks in 1,022 plays. In the first quarter of week seventeen against the Green Bay Packers, Mills suffered a fractured fifth metatarsal bone in his left foot when leaving the field, and required surgery.
Mills joined the Buffalo Bills midway through the 2015 season from the Detroit Lions practice squad. On March 11, 2017, Mills signed a two-year, $4 million contract extension with the Bills. He started all 16 games at right tackle for the Bills in 2017.
On September 10, 2019, Mills was signed by the Arizona Cardinals. He was placed on injured reserve on October 5 with a knee injury. He was designated for return from injured reserve on November 25, 2019, and began practicing with the team again. However, he was not activated by the end of the three-week practice window on December 16, 2019, and remained on injured reserve for the rest of the season.
