- School Eastern Illinois University
Johnson, who never played professionally, made his name as the pitching coach of Vanderbilt University for 11 years, from 2002 to 2012, during which he mentored future major league pitching stars David Price and Sonny Gray. He was promoted to associate head coach in 2010. He was named the National Pitching Coach of the Year in 2004 and the National Assistant Coach of the Year in 2010. During this time, the university reached the College World Series for the first time in its history in 2011.
Before joining the Vanderbilt coaching staff, he was a coach at Eastern Illinois University, where he had been a pitcher, in 1994. He then moved to an assistant coach position at Southern Illinois University in 1995, following head coach Dan Callahan who made the same move, staying for three years. He also managed in the Central Illinois Collegiate League in 1994 and 1995 and was a pitching coach for the Anchorage Glacier Pilots in 1996. In 1998, he moved to Stetson University as a pitching coach, working with future major league pitcher Lenny DiNardo.
His success at Vanderbilt led to a job in the Chicago Cubs organization as minor league pitching coordinator from 2013 to 2015. In 2016, he was hired as pitching coach by the Brewers when Craig Counsell, heading into his first full season as the team's manager, made a few changes to the coaching staff he had inherited from his predecessor, Ron Roenicke. He received a lot of praise for the significant improvement shown by the Brewers' pitchers in 2017 and again in 2018 when the team overcame the loss of a number of starting pitchers to still make it to Game 7 of the NLCS. However, he left the team only a couple of weeks later, in order to join the staff of new Cincinnati Reds manager David Bell in 2019.
He is the author of The Complete Guide to Pitching, an instructional manual first published in 2013. David Price wrote the book's foreword and has continued to consult with his former coach after leaving Vanderbilt.
- Derek Johnson: The Complete Guide to Pitching, Human Kinetics, Champaign, IL, 2013. ISBN 978-0736079013
- John Manuel: "Johnson Embraces New Challenges with Cubs", Baseball America, Nov. 16, 2013. 
- Adam McCalvy: "Brewers pitchers praise unsung hero Johnson: Pitching coach enters third season in Milwaukee after breakthrough 2017 season", mlb.com, February 14, 2018. 
- Adam McCalvy: "Crew eyes pitching coach as Johnson departs", mlb.com, October 31, 2018. 
- Carrie Muskat: "Johnson interested in what drives hurlers: Minor League pitching coordinator making jump to pros after 11 years at Vanderbilt", mlb.com, undated circa Oct. 2012.