Born 20 March 1858 to a Presbyterian minister, Mary Margaretta Campbell had a short but definite impact on mission work in northern Thailand.

While in her senior year of study at Western Female Seminary in Oxford, Ohio notices for young single female missionaries came to the school. A movement of the Holy Spirit convicted the hearts of these twelve young women, and both Edna Cole and Mary Margaretta Campbell volunteered and were selected to go to the Laos Mission field.

After receiving her appointment, Mary learned that Jonathan Wilson, a missionary of the Laos Mission and a friend and college classmate of her father, was to escort her to Chiang Mai. On 26 November 1878, after a two-month journey, their party arrived in Bangkok.

Upon arriving, the US Consul in Bangkok said: "You are too young to bury yourselves in that isolated field among the Laos; stay here and I will find a school for you, if you must teach." Mary answered, "Our youth is the best we have to give to Christ, and that is just why we are going. The best we have is not too good to give to Him who gave Himself for our sins, and the sins of this world."

On 19 April 1879, Mary arrived in Chiang Mai. She not only brought an ability to teach, but she also had a great talent in music and brought with her a guitar and organ. On their arrival, Mary and Edna took on the task of opening a Girl's School in Chiang Mai (later to become Dara Academy). May Campbell remarked in one letter that taking on such a difficult work without having taken at least a year of language study had been detrimental, but with the enormous task before them, they had little choice.

In late 1880, Mary Campbell traveled downriver to Bangkok. There she met her newly arrived friend and seminary classmate, Laura Olmstead, who would serve in Bangkok. A few weeks later, Dr. Cheek arrived in Bangkok to escort Campbell back north. On 8 February 1881, while returning north to Chiang Mai, Mary Campbell drowned.

To her parents, Jonathan Wilson wrote: "Your sorrow will be deepest, tenderest; my dear bereaved ones, what can I say to comfort you? Nothing, nothing. But I can remember and I will try to pray for you. Your dear Mary needs no longer your prayers. Her work is done-done well and she sleeps in Jesus - sleeps well."