He was born on February 28, 1940 in the Italian town of Montona on the Istrian Peninsula. After World War II, the Istrian Peninsula was stripped from Italy and given to Yugoslavia; his birthplace is now known as Motovun, Croatia. His family, like many Istrians fled under pressure from Tito's Communist regime, spending several years in a displaced persons camp. The Andretti family was eventually resettled in Nazareth, Pennsylvania. Andretti began racing cars in 1959, just after his family had moved to the United States. He made his debut in the USAC series in 1964, and won the championship the very next season.
He also started taking part in Formula One, and won his first race in 1971 for Ferrari. By the mid-1970s, Andretti started to focus on Formula One, driving for Colin Chapman's Lotus team. With the revolutionary "ground effect" car, Andretti won 6 races in 1978, and took the title.
He returned to Indycar in the 1980s, and won his fourth title in 1984. His last victory in that class came in 1993. Andretti kept racing to try and win the only important missing award - the 24 hours of Le Mans, but failed to do so.
Both of Mario Andretti's sons, Michael and Jeff, are also involved in auto racing, and Michael has won the Champ Car title as well. As of 2003 he is CART's winningest driver. Mario's nephew John has had success in both CART and NASCAR, winning races in both series, and his grandson Marco has won a championship in CART's "Stars of Tomorrow" kart racing series.