Ellen Elizabeth Colebrook is said to have been born on 14 March 1829 at Great Tangley Manor near Guildford, Surrey, England, and was baptised on 3 May 1829 at Guildford. She was the second of 17 children of Mary Ann May and her husband, William Colebrook, a tenant farmer. The family were fervent Methodists. Educated at a 'Seminary for Young Ladies' run by the Misses Priddie and Pattenden in Guildford, Ellen set up, with two sisters, a 'Boarding School for Young Ladies' in Guildford, in which she was sewing mistress. She married Oliver Sidney Ellis, a builder, at Islington, London, on 21 September 1852 and had three sons, John William, Alec and Thomas; Alec died in 1857. She arrived in Auckland, New Zealand, in July 1859 on the Whirlwind, with her husband, two sons, a brother, Tom, and a cousin, John. Oliver Ellis became involved in house-building and property speculation in Auckland until his death on 12 March 1883.
The marriage was not a happy one. Ellen Ellis disapproved of her husband's drinking and resented his refusal to let her handle money or to tell her anything about their financial situation; he disapproved of her opinions on the Māori and on the role of women. In January 1864 she returned to England to put her sons in school. Thomas drowned on the voyage. Leaving William in England, she returned to Auckland in February 1865 at her husband's request. He was facing bankruptcy, and she succeeded in rescuing him from his creditors. In the 1870s, with the encouragement of the Reverend Samuel Edger, she followed a programme of self-education and wrote a novel, Everything is possible to will, published in London in 1882. No reviews of the novel have been traced and her son bought up and burnt as many copies as possible.
The novel is autobiographical, avowedly feminist, and much concerned with social problems. The heroine, spirited and intelligent but limited by the poor education offered to girls, marries a businessman who turns out to be an alcoholic, and goes with him to New Zealand. The effects of alcoholism on the marriage and the family are vividly depicted, and the novel generalises about the evils of the liquor traffic and the servility of legal bondage of wife to husband. Ellen Ellis exposes the evils of drunkenness in men and advocates controls on the sale of alcohol. She also points out the necessity of good education and legal freedom for women to enable them to use their superior moral and emotional influence to gain these ends. Even without these advantages, women are slowly realising their power to influence public opinion by direct appeals to their own sex.
The novel also argues, in what is for its time an outspoken way, for birth control through abstinence: women must refuse to be sacrificed to the lusts of men. The heroine limits her family, refusing to follow the example of her mother who 'loved her husband…but she never could forgive him the suffering her 17 children had occasioned her; she felt instinctively that she had been cruelly wronged in being made to suffer so much for the selfish gratification of another'. While acknowledging that parents should limit family size to the number of children 'to whom they can do full justice', Ellen Ellis emphasises 'the martyrdom of maternity'. She argues that 'an amount of mock modesty highly reprehensible hangs about the population question' and attacks the medical profession for keeping women in ignorance. The novel ends on a note of appeal: 'Public opinion can, if it will, strike the chains of slavery from woman's intellect and heart, and make woman's emancipation the greatest trophy of Victoria's reign.'
With the outbreak of war in Taranaki in 1860, Ellen Ellis gave expression to her humanitarian views. She opposed the use of force to settle disputes and pleaded for women to 'band together to insist that there shall be no more war.' She showed her sympathy for the Māori by briefly attending Governor Thomas Gore Browne's conference at Kohimarama in 1860. An appendix to her novel explains the difficulty the Māori had in comprehending the selfish individualism of Europeans. And in a letter of 1860, she wrote of the damage the missionaries had done in preaching against tapu, which, she realised, was not only a matter of spiritual belief but a powerful regulatory force in Māori society. She had her sons taught Māori and believed the government had failed to realise the need to understand Māori culture.
Ellen Ellis's writings place her in the tradition of religious humanitarianism, but with a distinctively feminist perspective. When she died of 'bronchitis' in Auckland on 17 April 1895, the newspapers failed to accord her an obituary.