Badly injured on the family farm, Johnson turned to teaching to support himself.

After graduating from the University of Michigan, he moved to Chicago, Illinois, to attend Rush Medical College.

Receiving a Doctor of Medicine in 1852, Johnson was named Lecturer on Physiology at Rush, eventually chairing a department there.

When he was sixteen, Johnson sustained a grievous injury and was no longer able to perform manual labor.

[1] Upon graduation, Johnson moved to Flint, Michigan, and continued to study medicine while teaching.

In October 1850, he moved to Chicago, Illinois, to attend lectures at Rush Medical College.

Upon organization, Johnson was named president of the faculty and professor of materia media & therapeutics.

[1] That winter, his health failed again and despite a six-month sabbatical in Europe, Johnson was forced to retire from his professorship and department presidency.

The daughter died young, but the son, Frank Seward Johnson, followed his father into the medical profession.

He organized a Knights Templar chapter for Illinois and was first officer of that branch for two terms.

He became a member of the Supreme Council of the Scottish Rite Northern Jurisdiction in 1861, later becoming and officer.

Johnson died from pneumonia at his Chicago home on February 26, 1891, and was buried in Rosehill Cemetery.