Rachel Hull was born at Hokitika, New Zealand, on 23 July 1866, the daughter of Mary Ann Walters and her husband, James Hull. James, an American, was described as a musician when Rachel was born but later worked as an iron moulder in Christchurch. Rachel received her education at the Christchurch Normal School. On 17 October 1890 she married William Rae Don at the Durham Street Wesleyan Church in Christchurch. The couple made their home in Dunedin, where William Don was a stationer. There do not seem to have been any children of the marriage.
Both Rachel and William Don were actively involved with the Dunedin Methodist Central Mission, and were members of the quarterly meeting of the Dunedin circuit. William was also choirmaster for many years. Rachel was active on the sisterhood committee, which invited and supported deaconesses in the activities of the mission. By the early 1920s she was one of the best-known church workers in Dunedin.
In 1902, apart from the two deaconesses (who were entitled to attend the meeting), she was the only woman member. However, claims that she was the first woman to be licensed as a local preacher in the Methodist church in New Zealand have not been verified; in Dunedin, at least, it was not unusual for women to be local preachers. The Dons' association with the Methodist church ceased in 1926 when they transferred their membership to the Roslyn Presbyterian Church.
In the early 1900s Rachel Don became active in the temperance movement, especially through her membership of the Women's Christian Temperance Union of New Zealand (WCTU). She held the national executive positions of evangelistic superintendent and president of the Inner Family Circle, and from 1914 to 1926 was dominion president. In 1920 she represented the New Zealand WCTU at a world convention in London, and in 1924 attended the National Jubilee Convention in the United States. During this visit she was afforded the unusual honour for a non-American of being invited to speak before Congress.
Rachel Don gave talks, wrote letters and articles and produced cartoons in the campaign for social reform. While prohibition was her principal platform, she also lectured on foreign missions and evangelical work. With Jessie Field, she wrote a pamphlet in 1914 addressed to the men of New Zealand on the subject of the white slave traffic. She supported the appointment of women to the New Zealand Police Force and women's involvement in the judicial system in general. She also worked closely with Nellie Peryman, editor of the WCTU magazine the White Ribbon from 1913 to 1945.
Over the years Rachel Don also served on the ladies' auxiliary committee of the local YMCA, on the executive of the Otago Sunday School Union, and on the ladies' committee of the Otago Hospital and Charitable Aid Board. She was for a time official visitor to Dunedin Hospital, organiser of the Dunedin Stocking League, and a keen worker on behalf of the Ramabai Mukti Mission in India.
Rachel Don died in Dunedin Hospital on 4 September 1941, survived by her husband, William. She is remembered for her activity in the temperance movement, but along with other women preachers of her time is largely a forgotten figure in the history of the Methodist church in New Zealand. However, the acceptability of women such as Rachel Don helped to pave the way for the ordination of women in the Methodist church in the 1950s.