Mary Burnett Horton was born in Stirling, Scotland, in 1897 and moved to New York City with her family as a child. She graduated from Hunter College, where she trained as a bacteriologist. In 1920 she began working as a laboratory assistant at Sheffield Farms; she became chief bacteriologist in 1932. When Sheffield inaugurated a consumer education program in 1937, she became its director, developing school and public visiting programs at four major milk processing plants in greater New York, focusing on pasteurization and the nutrition of dairy products. With wartime restrictions in 1941, she took the programs to consumers, lecturing extensively to women's clubs on feeding families under food shortages and rationing. She served as chairperson of the Manhattan Nutrition Committee from 1944 to 1946, while earning a master's degree from New York University in Home Economics with a specialty in nutrition in 1946. In 1949 she became the only woman elected to the Board of Directors of Sheffield Farms, a post she held until 1956, when the company became a division of National Dairy.

In 1947 Horton was appointed director of National Dairy's Sealtest Consumer Service, which included four test kitchens equipped with the latest and newest appliances. The aim of the kitchens was to help consumers, dietitians, and school, hospital and industrial food managers to adjust to postwar changes, including the advent of convenience foods and the transfer of new technology to consumer products. The staff working in the kitchens performed extensive work on recipe development, culminating in recipe pamphlets, publicity releases and quantity recipe cards. During her fifteen years as director of Sealtest Consumer Service, Horton was widely regarded as an authority in home economics and a pioneer in the consumer and institutional education in the foods and nutrition field.

Mary Horton retired from Sealtest in 1962 but continued to be involved in various professional associations. In addition to her position at Sealtest, Mary Horton was the chairperson of New York City Home Economists in Business (1953), the American Home Economics Association, and the Consumer Services Committee of Grocery Manufacturers of America (1955-56). She served on the U.S. Navy Food Advisory Committee from 1948 to 1962. As consumer consultant editor of the trade publication Food Business from 1953 to 1963 she authored many articles in various publications.

Horton also served as the chairperson of civil service of the New York City Federation of Women's Clubs. She was appointed a member of the Women's Committee established in the late 1950s by Governor Rockefeller and the Department of Commerce whose purpose was to find ways to create careers for women. In 1963 she traveled to the Soviet Union as part of the American Home Economics Association to take part in a Women's Congress. Mary Horton died in 1974 at the age of 77.