Herman Merrills Johnson was born on November 25, 1815 in Butternut Township, New York, near Albany. He attended Casenovia Seminary and then went to Wesleyan University, where he was a member of Phi Beta Kappa and graduated with an A.B. degree in 1839. Following graduation, he became a professor of ancient languages at St. Charles College in Missouri until 1842. At that time he moved on to be a professor at Augusta College in Kentucky where he remained for only two years. In 1844, Johnson began teaching at Ohio Wesleyan University and would remain there until coming to Dickinson in 1850, when he took up the post of professor of English literature under the administrations of Jesse Truesdell Peck and Charles Collins. In 1852, Johnson was granted a D.D. degree from Ohio Wesleyan University.
During his ten years as a professor at Dickinson College, Johnson worked with three students to organize the “Eclectic Society of Dickinson College.” This society became active on May 12, 1852 as a chapter of Wesleyan University’s Phi Nu Theta, a fraternity to which Johnson belonged during his college days. This group marked the first fraternity at the College, but was soon followed by others such as Phi Kappa Sigma in 1854 and Sigma Chi in 1859.
Following Collins' resignation in 1860, Johnson was elected as the twelfth president of Dickinson College. Much of his presidential term was occupied with the effects that the American Civil War had on the College. At the outbreak of war, students from both sides left the College. Johnson moved swiftly, with the aid of Governor Andrew Curtin, to persuade the younger enlistees to return. Classes continued for the most part, but with some difficulty. In 1863, Lee's invasion of the North brought the town of Carlisle and the College under confederate shellfire and brief occupation in the days immediately preceding the battle at Gettysburg. Following the battle, federal authorities commandeered most college buildings for use as hospitals for the wounded of both sides. No students were present at this time since graduation had been hastily moved up before the action took place.
Following the war, the student body had lost most of its usual influx from the southern states and was only three-fourths of the size it had been in 1860. Johnson continued to battle the deficits which had plagued his entire presidency. He sought money constantly from the Methodist Conferences, and tried to modernize the curriculum to make the College more attractive. With the help of the science faculty, including the young and influential Charles Francis Himes, areas of study such as chemistry, geology, and metallurgy were incorporated into the program. A business school, known as the Dickinson Commercial College, operated as part of the College for a short time before moving to Hagerstown, Maryland.
The centenary of the Methodist Church in 1866 finally offered some relief by the significant endowment of new funds, although Johnson never saw their effects. Exhausted by his years of effort and virtual poverty, he contracted a cold and died two weeks later at his home in Carlisle on April 5, 1868. He had married Lucena Elizabeth Clark whom he met in New York during their education. She survived him, as did six of their seven children, one of whom was the novelist Mary Dillon, author of In Old Bellaire.