John Stuart Mill's philosophical contributions centered on utilitarianism, advocating for actions that promote the greatest happiness for the greatest number. His works advanced the idea of individual liberty, emphasizing that freedom should only be curtailed to prevent harm to others. Additionally, Mill argued for women's rights, becoming an early proponent of gender equality. His seminal work, "On Liberty," critiques societal norms and promotes the importance of personal autonomy. Through his advocacy for social reform and ethical analysis, Mill significantly shaped modern political and moral philosophy.