Barnard was a member of the team, headed by his brother Christiaan Barnard, that performed the world's first human-to-human heart transplant. Barnard was motivated by the financial hardship he saw his patients suffer after he had treated their critical illnesses to convince the South African insurance companies to introduce a new type of insurance to cover critical illnesses. Barnard argued that, as a medical doctor, he can repair a man physically, but only insurers can repair a patient's finances. On 6 October 1983 the first critical illness insurance policy was launched.
Marius Barnard was a member of the South African parliament between 1980 and 1989, in the party that opposed apartheid. He is currently semi-retired, acting as a technical consultant for Scottish Widows. Barnard has received many awards for his contributions to medicine and humanity, and was voted in the top 25 most influential people in the field of health insurance and protection.