Comaneci was born in OneÅŸti, Romania on 12 November 1961 and is the daughter of Gheorghe and Åžtefania-Alexandrina. Nadia is not a Romanian name; Comaneci's pregnant mother was watching a Russian film in which the heroine was called Nadya, the shortened version of the Russian name Nadyezhda (which means literally "Hope"), and decided that her daughter would be Nadia, too. Comaneci also has a younger brother named Adrian.

Comaneci began gymnastics at the age of 6. She first competed nationally within Romania in 1970, as a member of her hometown team. She was soon coached by Bela Karolyi and his wife Marta, who would later defect to the United States and become coaches of many great American gymnasts. As a 13-year-old, Comaneci's first major success was at the 1975 European Championships in Skien, Norway, where she won three gold medals (including the all-around title) and one silver. At the Pre-Olympics competition in Montreal in 1975 Nadia won the All-Around title. That same year the Associated Press named her their "Athlete of the Year."

At age 14, Comaneci became the star of the 1976 Summer Olympics in Montreal. Not only did she become the first gymnast at the Olympics to receive the perfect score of ten (which she repeated 6 more times), she also won three gold medals (individual all-around, balance beam and uneven bars), a silver medal (team all-around) and a bronze (floor exercise). Comaneci's main rival there was Nellie Kim, who also won three gold medals, overcoming Comaneci on the floor exercises, on the vault and winning the team gold. Comaneci said she was not surprised to receive her tens: after all, she had already earned 19 perfect scores in competition before Montreal. Back home, her success led her to be named a "Hero of Socialist Labor," the youngest Romanian to receive that recognition. She received this award while the country was under the brutal, Stalinist reign of Nicolae CeauÅŸescu.

Comaneci successfully defended her European all-around title in 1977, but the Romanian team controversially walked out of the competition during event finals to protest the scoring. An overweight and out of shape Comaneci showed up at the 1978 World Championships. A fall from uneven bars resulted in a 4th place finish, but she won the beam title.

In 1979, a newly slim Comaneci won her third consecutive European overall title (becoming the first gymnast, male or female, to do so). Comaneci's coach would have to tell her to cut down on the food just for her to stay in shape/petite at all times. At the World Championships that December, Comaneci led the field after the compulsory competition but was hospitalized prior to the optional portion of the team competition for blood poisoning due to a cut in her wrist from her metal grip buckle. Against doctors' orders, she left the hospital and competed on beam where she scored a 9.95. Her performance helped give the Romanians their first team gold medal.

She participated in Moscow 1980 Summer Olympics, placing second in the all-around to Yelena Davydova. Although many gymnastics fans have often considered this result controversial, Comaneci herself has never agreed. In her book she explains her defeat by writing "That day, Yelena just performed better" Comaneci retained her Olympic title in the balance beam, tied for the gold medal in the floor exercise, and her Romanian team finished second.

Comaneci retired from competition shortly after these Games. Her last major competition was at the World University Games in Bucharest in 1981 where she won 5 gold medals. However there were allegations of bias on the part of the judges as the Romanians themselves provided half the judges here. Whatever the case, there were some strange scores being thrown around at this meet: Comaneci scored a perfect 10 on a vault that was only worth 9.9!

Between 1984 and 1989, Comaneci was a member of the Romanian Gymnastics Federation and helped coach the Romanian junior gymnasts. In November of 1989, she defected to the United States. Comaneci spent most of her time touring and promoting lines of gymnastics apparel, Jockey underwear, aerobic equipment, and even modelled wedding dresses. In 1994, she was engaged to US gymnast Bart Conner and returned to Romania for the first time since her defection. Comaneci and Conner were married in Romania on April 27, 1996.

In 1999, Comaneci became the first athlete to be invited to speak at the United Nations to launch the Year 2000 International Year of Volunteers. She is currently busy with gymnastics and charity work around the world. She and her husband own the Bart Conner Gymnastics Academy, Perfect 10 Production Company and several sports equipment shops, and they are editors of International Gymnast magazine. Comaneci and Conner have also provided television commentary for many gymnastics meets, most recently the 2005 World Championships in Melbourne.

On June 29, 2001, she became a naturalized citizen of the United States.

Comaneci is Vice-Chair of the Board Of Directors of International Special Olympics, Honorary President of Romanian Gymnastics Federation, Honorary President of Romanian Olympic Committee, Ambassador of Sports of Romania, Vice President of the Board of Directors of the Muscular Dystrophy Association and a Member of International Gymnastics Federation Foundation. She has received two Olympic Order awards from the IOC. She was inducted into the International Gymnastics Hall of Fame In addition, Comaneci has started a charity clinic in Bucharest to help orphaned children in Romania.

In December 2003, her book, Letters To A Young Gymnast ISBN 0465012760, was published. The book answers questions that she has received in letters from fans.

On February 7, 2006, Comaneci and husband Bart Conner announced they are expecting a son to be born in July.