A legendary prep coach in the state of Maryland, Johnson was a six-time coach-of-the-year, and architect of one of the winningest football programs in the Maryland public school system. From 1977 to 1991, Johnson's teams at Maurice J. McDonough High School in Pomfret, Maryland were annually ranked among the top squads in the Washington, DC metropolitan area. In his final eight years, the Ram dynasty amassed an 82-10 record, made eight consecutive appearances in the state playoffs, were 8–2 in championship games and captured three Division 3A state championships. His overall record as head coach was 139–36. From 1992 to 1993, Johnson was head coach at T. C. Williams High School in Alexandria, Virginia. He was hired by his brother AK Johnson, the school's athletic director.
College coaching career
Johnson was the defensive line coach at Penn State from 2000 to 2013. From 1996 to 1999 he served as the Nittany Lions'defensive ends and special teams coach. In that time, Johnson developed a reputation for being a premier blue chip recruiter, consistently landing top talent from the mid-Atlantic states. He was instrumental in the development of five first-team All-Americans there: Devon Still, first-round NFL draft choices Tamba Hali, Michael Haynes, and Jimmy Kennedy, and former first-overall selection Courtney Brown. Johnson was offered the defensive coordinator and assistant head coach job at Illinois in January 2009. He ultimately decided to continue at Penn State. On November 10, 2011 Tom Bradley announced that Johnson and linebackers coachRon Vanderlinden would serve as co-defensive coordinators. On January 7, 2012, Johnson was retained as a coach on the team's staff with the arrival of new head coach Bill O'Brien. On January 1, 2014, Johnson was named interim head coach after O'Brien's departure to the NFL. Later that month, Johnson left Penn State after 18 years when he was hired by Ohio State to be an assistant head coach and defensive line coach. At Ohio State, Johnson is known for his ability to develop several highly-touted NFL prospects, including Joey Bosa, Nick Bosa, and Chase Young.
Personal
Johnson maintains a very close relationship with his son Larry Jr., who has repeatedly referred to his father as his "best friend" and "the only person in the world he completely trusts" in interviews. Johnson's other son, Tony, was a starting wide receiver for Penn State from 2000–2003.