Haslam began his career at Pilot Corporation in 1976. In 1980, Haslam was named vice President of sales, development and operations. At that time, Pilot operated 100 convenience stores with annual fuel sales of about 125 million gallons. Pilot opened its first travel center in 1981, and by 1996 – the same year Haslam was named President and chief executive officer – the company operated 96 travel centers and 50 convenience stores and its total gallon sales had reached 1.2 billion. Pilot Corporation attained yet another milestone in 2001 when it joined with Marathon Ashland Petroleum LLC to form Pilot Travel Centers LLC.
Haslam was inducted into the Junior Achievement of East Tennessee Business Hall of Fame in 2007, and in 2010, he was named a recipient of the Ernst & Young Entrepreneur Of The Year award for the Southeast region. In 2013, the University of Tennessee recognized Haslam with the Distinguished Alumnus Award. He is the co-founder of the Haslam Scholars Program for premier honor students at the University of Tennessee.
Haslam bought a minority interest in the Pittsburgh Steelers in 2008. In 2012, he reached an agreement with Browns owner Randy Lerner to purchase the franchise for $1 billion. The Browns were valued at $977 million in 2011 by Forbes magazine, 20th in the NFL. NFL rules prohibit ownership in multiple teams and so Haslam sold his interest in the Steelers. The Haslams' purchase of the Browns was unanimously approved by the 32 teams in the NFL on October 12; the sale itself closed thirteen days later.
Since officially taking over the Browns seven games into the 2012 season, Haslam has a 20-76 record as team owner, including an 0-16 record in 2017.
In April 2013, the FBI executed a search warrant and affidavit detailing a five-year fraud scheme by the Pilot Flying J chain. The company paid restitution to customers and agreed to pay a $92 million penalty pursuant to a Criminal Enforcement Agreement.