Comăneci was discovered by Bela Karolyi, later the Romanian gymnastics coach, when she was six years old. She first competed in the national junior championships in 1969, placing 13th, and she won the competition in 1970. In her first international competition, in 1972, a pre-Olympic junior meet for the communist-bloc countries, she won three gold medals, and in 1973 and 1974 she was all-around junior champion. In her first international competition as a senior, in 1975, she bested the Russian Lyudmila Turishcheva, the five-time European champion, winning four gold medals and one silver. She won the American Cup in New York City in 1976, becoming the first woman to perform a backward double salto as a dismount from the uneven parallel bars.

At the 1976 Olympic Games in Montreal, Comăneci received seven perfect scores and won the gold medals for the balance beam, the uneven bars, and the all-around individual competition. She won a silver medal as a member of her team and a bronze medal for the floor exercises.