McCallum graduated from Northeast Louisiana University in 1982 and received a J.D. from Louisiana State University's Paul M. Hebert Law Center in 1985. McCallum worked with the law firm of Rabun and McCallum. He was also an assistant district attorney. McCallum served in the Louisiana House of Representatives from 1992 to 2002. He represented District 12 as a Democrat. He was then a judge on Louisiana's 3rd Judicial District Court as a Democrat until 2014, when he ran for re-election under no party and won. In 2018, he was elected unopposed to the 2nd Circuit Court of Appeal under no party. In 2020, he won a special election to the state supreme court as a Republican. McCallum has also given lectures at law enforcement academies and presentations for continuing legal education.
