Mary Jane McLean was born on 4 April 1866 at Timaru, New Zealand, the eldest child of Ann le Ber and her husband, Duncan McLean, a physician and surgeon. After attending Timaru Main School and Timaru High School Mary undertook several years of extramural university studies while teaching part time at Timaru High School. From 1886 she attended lectures at Canterbury College, boarding first in the home of Professor C. H. H. Cook, then from 1887 to 1889 as a resident teacher at the private Montfleuri Girls' School. She completed the BA course in 1888, taking college honours in botany and biology, and graduated MA with honours in Latin and English in April 1890. She was then appointed first assistant teacher of Timaru High School in 1890, during the reorganisation that followed George Hogben's appointment as rector in May 1889.
When the school was divided in 1898 she became principal of Timaru Girls' High School. Mary McLean was ambitious and began applying for girls' school principalships in the larger centres, probably as early as 1892. In 1900, against a strong New Zealand and Australian field, she won the principalship of Wellington Girls' High School (renamed Wellington Girls' College in 1905). She lived in Wellington for the rest of her life.
Mary McLean arrived with a vision of building a great school. Her brother Henry had preceded her to Wellington to set up in medical practice, and so too had George Hogben, appointed inspector general of schools in 1899. Both men, and also her father, probably helped to inspire the public-spirited, progressive professionalism that Mary brought to her task. Hogben's strong endorsement and other testimonials from the leaders of Timaru's educational establishment and the Canterbury College professors give a picture of a dedicated and gifted teacher, experienced in a wide range of subjects, with a developed philosophy of education and broad extramural interests. The school also gained an able and hardworking administrator and an institutional leader of real flair.
Mary McLean inherited a declining roll, inadequate facilities and endowments, and a board which persisted in favouring Wellington College for boys. Fortunately she was in tune with the sweeping secondary school reforms which Hogben was directing. She combined a high regard for academic excellence with a concern for the needs of the less academic pupils, who from 1911 flocked into the school under the new free-place regulations. She quickly enriched the curriculum with new work in drawing, class singing and gymnastics, and greatly improved science teaching. Because of lack of room and resources the school could not accept all the free-place pupils offering, but the roll grew steadily from 87 in 1900 to 339 in 1914.
In turning Wellington Girls' into a great school, McLean drew her inspiration from two main sources. The first was her deep Christian faith (she was a Presbyterian). This led to the Christian Union, a social and philanthropic club which she strongly supported, being the most potent element in the school's extra-curricular programme. To keep in touch with the fountain-heads of educational thought, she took a year's leave in both 1907 and 1918 to visit Britain, the Continent and North America. Her educational thought was closely akin to the progressive conservatism of the best British public schools, her second source of inspiration. The evidence she gave to the 1912 Education Commission is a good example of this outlook. She advocated equal opportunities for girls (including something to match the Rhodes scholarships), Bible in schools at all levels, accrediting in place of examinations (even for matriculation), and a university chair for a professor qualified to give the government expert economic advice.
Mary McLean fought long and hard, but with varying success, for the quality buildings and boarding houses, the preparatory department, the playing fields and sports tradition of the English public school model. With a burgeoning roll threatening to overwhelm the facilities, she played a major part in the establishment of Wellington East Girls' College in 1925. When she retired in June 1926 from a well-organised modern school of 850 she was given a civic farewell in a packed town hall. In 1928 she travelled to London to receive the CBE at Buckingham Palace.
Returning to Wellington McLean found renewed expression for her moral and social vision, particularly through the Women's Social Progress Movement, which she founded in 1929. Enlisting the aid of the wives of national and civic leaders, the movement campaigned on such issues as temperance, censorship and women's representation, by such means as political lobbying, public meetings and home discussion groups. In the depression years of the 1930s it also took up relief issues and activities. It faded rapidly when the New Zealand Labour Party's 1935 victory brought a new government to power.
For most of her years in Wellington Mary lived with her bachelor brother, Henry, and her unmarried sister, Agnes, both of whom predeceased her. She died at her home on 9 February 1949.