Johnson received his undergraduate degree from Augustana College in Rock Island, Illinois, where he earned Phi Beta Kappa honors.
In 1963, he graduated from North Park Theological Seminary in Chicago, Illinois and became an ordained minister with the Evangelical Covenant Church.
He also hosted "House Call", a half-hour weekly series on answering health-related questions from viewers and interviewing doctors and nurses on various health topics.
Currently, Dr. Jennifer Ashton is the Chief Medical Editor for ABC News; however, Johnson still serves as a correspondent.
Typically, though not exclusively, Ashton reports on developments in nutrition and pediatrics, while Johnson focuses on health issues for senior adults.