Morrison was elected as a Sinn Féin Member for Mid Ulster of a short-lived Northern Ireland Assembly from 1982 to 1986. He also stood unsuccessfully for the European Parliament in 1984, receiving 91,476 votes and again in 1989. He also stood for the Mid Ulster Westminster seat in 1983 and 1986. Morrison, along with Owen Carron, was arrested on 21 January 1982 whilst attempting to enter the United States illegally from Canada by car. He was deported and later both men were convicted on a charge of making false statements to US immigration officials.