Howard Campbell was born in Moniteau, Pennsylvania, on October 12, 1866. He graduated from Grove City College in 1891. He went on to study theology at McCormick Theological Seminary and later at Western Theological Seminary, graduating in 1894. Campbell married Sarah Elizabeth Carlton of Volant, Pennsylvania, on June 19, 1894. Within two months, the two newlyweds left the US for their assignment as missionaries in Chiang Mai, Thailand.

Throughout Campbell’s 42 years of missionary service, his most significant role was the influential discipleship work he helped create and lead in northern Thailand. From 1899-1910, there was no structured theological training in north Thailand. Campbell would go and do extensive teaching among elders and church leaders in the surrounding village churches in the Chiang Mai region. These itinerant trips would be in three-month durations and became an annual event for the Campbell family.

All his colleagues in the Laos Mission admired Campbell. When there were small animosities between factions, Campbell played a critical role as a friend to all. With this trust, Campbell was often selected to take on challenging tasks. In 1904, Campbell visited the Kamu Christians, during a time when the French government did not welcome American missionaries. In 1907, Campbell, along with Dr. Samuel Peoples, was selected to help solve the comity question of whether the Laos Mission should continue to hold a station in Keng Tung, Shan State. This question was a strong point of contention between the American Baptist and Presbyterian Missions.

On February 25, 1920, Sarah Campbell died in Chiang Mai, Thailand. Campbell returned to the US for a short furlough. While in the US, he met and remarried Mary Guy Shellman, on May 20, 1922. Mary was the widowed wife of a missionary who had previously served in Siam. Mary played a substantial role in assisting her husband in his ministry and leading many significant Christian social events. The two served until honorably retiring in 1936. On October 14, 1957, Howard Campell died in Duarte, California. He was followed in death by his second wife, Mary, who died on June 28, 1962.