Was the British abolition of slavery and the slave trade a triumph of altruism over pecuniary self-interest? Analysis of qualitative data reveals the importance of self-interested motives underlying this ostensibly other-regarding reform. The abolitionists worked to alleviate the suffering of enslaved Africans, but their campaign faced a collective action problem that was solved by the supply of the private benefits of status, esteem, and possible religious salvation to the leading figures. Abolition was also consistent with the desire of many ordinary Britons to eradicate the remnants of feudal society and move to a more liberal order. The payment of compensation to slaveowners on abolition also made reform consistent with their interests, and the interests of the individuals and financial institutions that processed and invested the payments. This analysis coheres with aspects of Eric Williams’ thesis that abolition took place because it benefited Britain’s ruling elite, although more Britons gained from abolition than Williams supposed. It is concluded that constitutional reform to remove oppressive and exploitative institutions does not follow from a sudden outpouring of societal altruism but requires the supply of private benefits to constitutional entrepreneurs able to make change consistent with the interests of the wider population and powerful groups who would otherwise lose from liberalization.