Esther Mary Baber was born at Christchurch, New Zealand, on 21 March 1871, the daughter of English parents Jane Wood and her husband, Thomas Primrose Baber, a corn merchant. Esther and a younger sister grew up in a modest and orderly home free from strain. Their father shared his knowledge of architecture and his love of the countryside and their mother impressed them with her strong sense of duty. Esther was taught by tutors until near matriculation and then went to Christchurch Girls' High School to finish her schooling. She attended Canterbury College and graduated MA from the University of New Zealand in 1898. Her student acquaintances included S. Arnold Atkinson, Frank Milner, Apirana Ngata and Ernest Rutherford.
After relieving the French teacher for a year at her old school Esther Baber went to Wellington in 1897. She and Beatrice Richmond, who was on the staff of Mary Anne Swainson's Fitzherbert Terrace School, held coaching classes before taking charge of the day school. After Swainson's death in August 1897 the two women established their own school, the Pipitea Private School, which they ran from 1899 to 1906. Baber also took several boarders into her home.
Within 18 months in 1904–5 Esther Baber's parents and sister died. She gave up the school and in 1906 visited England and Europe. While she was away her lawyer friend Arnold Atkinson arranged for her to buy the Fitzherbert Terrace School from Mary Anne Swainson's daughter, Mary Jessy Swainson. So began, in 1907, with 30 day girls and 17 boarders, the school that would flourish under her hand for 25 years.
Victorian though Baber's sense of discipline and decorum were, in her understanding of education she was far ahead of her time. She favoured the ideals of the Froebel Society, encouraging her pupils to develop a sense of inner harmony in their lives by discovering the underlying unity of all things through creative activity. The school had a close association with the Anglican church but Baber welcomed children of all creeds. Well read herself, she established a library in 1907 and every year's study was focused on a central theme. Current events were discussed and social concerns acted upon. She was openly critical of the rigid curriculum imposed by the contemporary matriculation examinations, and firmly believed that a girl needed 'quiet development' and should not leave school before she was 18. To teach music and the arts her staff included Robert Parker and Dorothy Richmond.
As well as high ideals and integrity, Esther Baber had a good understanding of motives and behaviour. She did not resort to sarcasm and had a quick sense of humour. Although not tall she was a dignified and attractive figure with keen bright eyes, trim black hair and a fine voice. Her extraordinary vitality and quiet warmth were readily conveyed to her pupils and made her school a very friendly place. The extent of her influence was expressed by a pupil in 1911 in the statement, 'Miss Baber is the School'.
Baber's own creative spirit was enriched by three further trips to Europe. Her recreation centred on her cottages at Hampden, Otago, and at York Bay near Wellington among the Richmond and Atkinson families. Picnics and the care of her garden and home were particular pleasures, often shared with senior girls, many of whom remained her friends for life. She founded the old girls' association in 1912. In the wider community she was on the committee of the Wellington Diocesan Church Schools Board, a life vice president of the St Mary's Guild and a member of the Women Students' Hostel Society of Victoria University College.
In 1920 Esther Baber sold her school to the diocese of Wellington. The diocese had been offered 10 acres in Karori by the Riddiford family on condition it bought the school. Baber continued as headmistress and the school was renamed the Samuel Marsden Collegiate School. In 1926 it shifted to Karori. A parents' association was formed in the same year. Baber regarded the founders' assembly hall, which opened at the new site in 1930, as the school's 'very heart and centre'. However, the move to Karori took its toll on Baber's health. She resigned as headmistress in 1931 but was a member of the school's board of governors from 1932 to 1956. After her retirement she built a house at Silverstream. She visited the school regularly and made friends with each year's new pupils. In 1951, on her 80th birthday, she was the guest of honour at a party put on by the old girls of the school.
Esther Baber died at the Kirkleigh nursing home in Karori on 19 November 1956 at the age of 85. Her funeral service was held at St Paul's Cathedral Church which she had attended for most of her years in Wellington. She had never married and left a legacy of over £6,000 for the Marsden school's chapel fund.