John Stuart Mill was the 'Saint of Rationalism' according to William Gladstone. But in the first definitive biography of Britain's greatest public intellectual, Richard Reeves reveals Mill as a passionate man of action: a philosopher, radical MP and reformer who profoundly shaped Victorian society and continues to illuminate our own. A young activist and highly-educated Cambridge Union debater, Mill would become in time the highest-ranked English thinker of the nineteenth century, the author of the landmark essay On Liberty and one of the most passionate reformers and advocates of his revolutionary, opinionated age. As a journalist he fired off a weekly article on Irish land reform as the people of that nation starved, as an MP he introduced the first vote on women's suffrage, fought to preserve free-speech and opposed slavery, and, in his private life, pursued for two decades a love affair with another man's wife. Mill also fearlessly tackled issues such as domestic violence and the regulation of prostitution. To understand Mill and his contribution, Richard Reeves explores his life and work in tandem. His book is a riveting and authoritative biography of a man raised to promote happiness, whose life was spent in the pursuit of truth and liberty for all.