After learning and mastering the Hawaiian language, he won the confidence of the Hawaiians and converted thousands to Christianity. He set up schools, as did his wife, and provided medical assistance and comfort to a rapidly changing culture. He later established churches and trained native converts to act as missionaries among their own people.

He traveled extensively, and at times with great peril, throughout his island home and later to the Marquesas Islands. His adventures and descriptions of first-time encounters with both the environment and the people are quite remarkable. This was a time of great excitement and great despair. Foreign interests in Hawaii, military engagements, visitors of renown, and Hawaiian Kings all provide a rather colorful backdrop against which his story is told.

In addition to his missionary labors, Titus Coan added a great deal to our knowledge of volcanic eruptions. He corresponded and worked with geologist James Dwight Dana, performed many observations, and published with the American Journal of Science. For decades he explored and recorded the volcanic activity on the island of Hawaii.

Titus Coan is perhaps best known for his books Adventures in Patagonia (1880) and Life in Hawaii (1882).