In 1989 the Sunday Times asked Murray to investigate whether we had an "underclass". In 1999 they brought him back to review progress, with Underclass +10. In 1989 he had used three measures: drop-out from the labour force among young males, violent crime, and births to unmarried women. He thought they were associated with the growth of a class of "violent, unsocialised people who, if they become sufficiently numerous, will fundamentally degrade the life of society". In 1999 formerly law-abiding Britain had become "just another high-crime industrialised country". The underclass was "driven by the breakdown in socialisation of the young, which in turn is driven by the breakdown of the family", but the government was not even willing to state that the family was important.

He is least known for his most outstanding book, Human Accomplishment, where he described the main human achievements from 800BC to 1950 in music, literature, the visual arts, medicine and the physical sciences, explaining why Western culture had been more successful than others.

Murray will be remembered as one of the great champions of liberty. His new book, Coming Apart: The State of White America 1960-2010, develops his argument that class divisions have weakened American civic culture. A new elite cut off from middle-class America is emerging, while a growing lower class rejects mainstream commitments to work, religious faith, marriage and respect for the law.