William Thompson (1775 – 28 March 1833) was an Irish political and philosophical writer and social reformer, developing from utilitarianism into an early critic of capitalist exploitation whose ideas influenced the cooperative, trade union and Chartist movements as well as Karl Marx.

Born into the Anglo-Irish Ascendancy of wealthy landowners and merchants of Cork society, his attempt to will his estate to the cooperative movement after his death sparked a long court case as his family fought successfully to have the will annulled.[1] According to E. T. Craig, this decision to will his estate to the cooperative movement was taken after a visit to the pioneering Ralahine Commune.

Marxist James Connolly described him as the "first Irish socialist" and a forerunner to Marx, who cited Thompson in his works as well as being an influence upon Marx's thought.