Mary Barrett was born in London, England in 1873. She received a B.A. from University College, Liverpool in 1892 and then studied at Cambridge. In 1895 she married Dr. Henry Speechly. She joined Henry in Pilot Mound, Manitoba. Within the next year she began work as the Secretary-Treasurer of the Anglican Church. In 1912 she became president of the Pilot Mound Home Economics Society and was an advocate of home economics and domestic science.

In 1916 she moved to Winnipeg with her children while her husband served overseas. She was a member of the Agricultural Women's Association, the Women's Institute of Manitoba, the University Women's Club, and the head of the Women's Canadian Club. As the Treasurer and then President of the Winnipeg Red Cross she later acted as the first Director of the Manitoba Junior Red Cross. In 1924 she was appointed to the council of the Manitoba Agricultural College. She helped found the Family Planning Association of Manitoba and became the first president of the Winnipeg Birth Control Society in 1934. Speechly was appointed the first female member of the Board of Governors of the University of Manitoba in 1933 where she served until her retirement in 1946. In 1947 she received an Honorary Degree of Doctor of Laws (L.L.D.) from the University of Manitoba. She died in Winnipeg in 1968.