Morrison was the son of a Scottish farmer, born in the small village of Torinturk, Argyll. He attended George Watson's College and then went on to the University of Edinburgh; his studies were interrupted by World War I, where he served with the Royal Field Artillery and won the Military Cross. Training as a lawyer, Morrison was called to the bar in 1923 and began working as a private secretary to Thomas Inskip, the Solicitor General. After several previous attempts, he was elected to the House of Commons in 1929, representing a constituency in Gloucestershire for the Conservative Party.