Saint was sent out by the Wycliffe Bible Translators, trained by Summer Institute of Linguistics (now SIL International). Her first missionary assignment was to the Piro and Shapira in Peru, but she had an interest in the Huaorani in Ecuador. In February 1955, she and Catherine Peeke went to a missionary station near Huaorani territory, where Saint's brother was working. Rachel Saint started learning the Huaorani language with the help of Dayuma, a Huaorani woman who had left her people after a dispute and was sheltered by missionaries.