Born in Pentonville, London, in 1806, Mill was schooled from a very early age by his prominent father, James Mill, and his father's friends, including Jeremy Bentham. By the age of seven, he was reading Plato and by the age of 8 was learning Latin. At the age of thirteen, Mill underwent a complete course in political economy and spent a year living in France with General Samuel Bentham, where he met the famed economist Jean-Baptiste Say.

At the age of sixteen, John gained an appointment as a clerk in the office of the Examiner of India Correspondence at the East India Company. He would continue to work for the East India Company until its dissolution in 1858. In 1823, at the age of 17, Mill adopted Utilitarian ideals and started a discussion group known as the Utilitarian Society.
As a budding philosopher, economist, and employee of the East India Company, Mill's career was interrupted when, in 1826, he suffered an acute mental crisis. Mill felt that the reforms he sought in the economy and society would not bring him lasting satisfaction and that logical analysis, which he had become mechanistically proficient at, dissolved the associations that he formed through his education. His habit of analysis had weakened his feelings and emotions to the point that he could not feel. Mill described himself as experiencing "dry heavy dejection" toward the end of 1826 in his autobiography. By the late 1820's, Mill emerged from his general depression with a new self-awareness and revised outlook on the importance of emotions.
While continually publishing various works in many journals, Mill founded the London Review with William Moleworth in 1834. He later merged this journal with Jeremy Bentham's radical quarterly journal, Westminster Review, which he purchased in 1836. Other newspapers and journals he wrote for included the Morning Chronicle and Parliamentary History & Review.
Mill published his first large book, System of Logic, in 1843. System of Logic was Mill's attempt to give an account of scientific methods and their social and societal application, as well as to natural phenomena. It was in this book that Mill defined psychology as the "science of the elementary laws of the mind," a definition later adopted by Titchener. This stood in direct opposition to Auguste Comte's and Immanuel Kant's views that the phenomena of the mind could not be studied. Mill admitted that psychology would be an inexact science, but felt the only way to remedy psychology's backward state at the time was to apply the scientific method of natural sciences. He followed this with Principles of Political Economy in 1848, in an attempt to rid economics of the notion that it was a "dismal science," as was the popular sentiment at the time. It was a huge success and sold over 1000 copies in the first year and was reprinted in 1849.

In 1854, three years after his marriage to the widow Harriet Taylor, Mill began work on his essay On Liberty, influenced by the sentiment that he and his wife shared regarding the growing scarcity of bold and adventurous individuals. In this essay, which he expanded in 1857 and published two years later, Mill argued that the domination of public opinion and the power it wields is endangering individual freedoms.
In 1856, Mill was promoted to Examiner of India Correspondence for the East India Company. He held that office until the British government took over control of the company following a mutiny two years later.
In 1863, Mill published Utilitarianism, the quintessential resource for the belief in the pursuit of the most happiness for the greatest number of people. It built upon Bentham's notions of hedonism, but added what hedonism lacked, such as compassion, love of beauty, sympathy, and dignity. Mill felt that the degree to which an action can be considered wrong or amoral can be measured by the degree to which it creates unhappiness in others, a philosophy that gained much support in the 18th century and continues to have support today.
In 1865, Mill was elected to the Westminster seat in Parliament as a Radical. He remained a force in parliamentary procedures, campaigning for parliamentary reform and women's suffrage, as well as amending bills in an attempt to give women the same political rights as men, until he lost the election in 1868 after losing popularity by voicing disapproval of the colonization of the West Indies.
Following his work for equality of the sexes in Parliament, Mill became one of the first prominent male feminists. His publication of the Subjection of Women in 1869 is often considered a classical statement of liberal feminism. In this book, Mill argues that the freedom that is a good for men must also be for women and that arguments concerning differing natures of the sexes are nothing more than superstition. Though he had begun work on Subjection of Women as early as 1860, he waited until later to publish so as to avoid controversies that might detract from his other works.
Already established by 1873 as one of the leading intellectual and philosophical thinkers of his time, the Autobiography of John Stuart Mill was published in the same year that he passed away in Avignon, France, with his stepdaughter at his side.