Gunn became a Presbyterian missionary involved in work to the Philippines, South China and Hawaii. He served as executive secretary of the Layman's Missionary Movement in 1909 and was the Philippines mission architect from 1916–1921. As the Presbyterian representative in the[Missions Architects Bureau, he supervised the construction of the Missions Building located at 169 Yuanmingyuan Road in Shanghai. His daughter Harriet married Presbyterian missionary Roger Cumberland, who was shot dead in N Iraq in 1938. This understandably seems to have altered the course of Charles and his wife's lives. Finally in 1940 he was an instructor at the American University of Cairo, Egypt before returning to the United States, where they had responsibilities towards their widowed daughter and two fatherless granddaughters. [2]