Lavergne earned a bachelor of arts degree in social studies education and a master's in education at the University of Louisiana at Lafayette. In 1988, he earned an education specialist degree in educational administration and supervision from McNeese State University. He was a social studies teacher, held administrative positions for both the SAT and the ACT college entrance exam companies, and in between jobs performed stand-up comedy. He worked for the College Board traveling to universities helping administrators understand the SAT. Lavergne retired as director of admissions research for the University of Texas in 2019. Among Lavergne's books is 1997's A Sniper in the Tower about the 1966 shooting rampage of Charles Whitman, which according to a 2007 Associated Press article is "considered the definitive account of the massacre" and to Frank Rich in a 1997 The New York Times piece is "the authoritative account of the Whitman case".
- Before Brown (2010), about the struggle for civil rights in higher education, centered on the Sweatt v. Painter case at the University of Texas at Austin.
- Worse than Death (2003), about Moroccan national Abdelkrim Belachheb, who walked into a Dallas nightclub and gunned down seven people. Published by UNT Press.
- Bad Boy from Rosebud (1999), about serial killer Kenneth McDuff. Published by UNT Press.
- A Sniper in the Tower (1997), about Charles Whitman, who shot people from the University of Texas at Austin's tower in 1966. Published by UNT Press.
- "Family of Gary Mitchell Lavergne and Laura Gwen Clayton". Gary M. Lavergne. accessed June 10, 2015
- Rich, Frank (1999-09-25). "Journal; The Long Shadow of the Texas Sniper". New York Times.
- Associated Press (April 25, 2007). "Campus killings tarnished Kent State, Texas". Reading Eagle. Retrieved 2010-02-19.