McCullough graduated from Sapulpa High School in 1985 and earned a bachelor's degree in agriculture from Oklahoma State University (OSU) in 1989.

Mark McCullough earned a JD in 1998 from the University of Tulsa College of Law and served as an Assistant Attorney General of Illinois.

Upon being elected to the legislature in 2006, McCullough opened up a solo law practice in Sapulpa concentrating in estate planning.

McCullough won the primary and advanced to the general election where he defeated Democratic Party candidate Melinda Johnson Ryan.

In 2010 general election, McCullough received the largest percentage of vote for a Republican in the history of the district, defeating Donna Marie Vogelpohl 76 to 24 percent.