Hartline attended GlenOak High School, where he both played football and ran track for four years. He began his football career as a quarterback, but in the fourth game of his sophomore year, he switched positions to wide receiver. Hartline was also on the GlenOak track team, and he was the 2005 state champion in the 110 metres hurdles and the 300 metres hurdles.
College career
Hartline redshirted his freshman year, but played in all 13 contests in 2006. In 2007, Hartline played an integral part in getting the Buckeyes to the 2008 BCS National Championship Game, averaging 13.3 yards per reception with 52 catches for 694 yards. In 2008, his final season, Hartline averaged 22.8 yards per reception with 21 catches for 479 yards. He graduated from Ohio State in June 2009 with a degree in Communications, but elected to forgo his final season of eligibility to enter the 2009 NFL Draft.
Professional career
Miami Dolphins
Hartline was drafted by the Miami Dolphins in the fourth round of the 2009 NFL Draft. On October 4, 2009, Hartline caught his first career touchdown on a 2-yard pass from Chad Henne. Hartline finished his rookie season with 31 receptions and 506 receiving yards with three touchdown receptions plus a rushing touchdown on a 16-yard play against the Pittsburgh Steelers. Although he finished third on the team in receiving yards, Hartline led the team in receiving touchdowns. After a solid rookie season in which played in every game, in the 2010 season, Hartline played only 12 games, although despite this, he had a better season statistically, with 43 receptions for 615 yards and 1 touchdown. He also rushed for 27 yards on 2 carries. After the release of Ted Ginn Jr. in the 2011 off season, Hartline cemented his place as a starter, starting in every game of the season. He recorded statistics of 549 yards from 35 receptions, thrown by Chad Henne at the start of the season, but after the former Michigan QB's injury, backup Matt Moore took over, leading to Henne's release in 2012. Despite struggling with injuries and illnesses during the off-season and training camp, Hartline played in the 2012 season opener against the Houston Texans and became the team's number one receiver with Brandon Marshall's trade. In a Week 4 loss against the Arizona Cardinals, he broke the Dolphins franchise record for receiving yards in a game with 253. He called the record "bittersweet" because his team lost the game. After that week 4 performance, Hartline led the NFL in receiving yards. Hartline eclipsed 1,000 receiving yards, becoming the eighth receiver in Dolphins franchise history to accomplish the milestone. During the offseason in 2013, Hartline stayed with the Dolphins, signing a 5-year, $31 million contract, with $12.5 million guaranteed. Hartline suffered a torn PCL in the last regular season game against the New York Jets in 2014, which forced him to end his season. He led the team in receptions with 76, which is also a career-high, and finished his second consecutive year with over 1,000 receiving yards.
Cleveland Browns
Hartline signed with the Cleveland Browns on March 9, 2015. On May 23, 2016, Hartline was released by the Browns.
