In 1853 he offered his services to the London Missionary Society and after two years' training was ordained in 1855 at Ebenezer, Swansea. That same year he married his first wife, Margaret Jane, a daughter of the Christian missionary, David Griffiths. After he was ordained, he wanted to serve in Madagascar but was instead persuaded by the London Missionary Society to go to China. The newly wed couple made the voyage to Shanghai arriving in September 1855. Griffith John would serve in China for 55 years, chiefly in Hubei and Hunan.