Born in Prague and originally a figure skater, she debuted internationally at the 1958 World Championships, winning a silver medal in the team event. She first participated in the Olympics in 1960, also winning a silver medal with the Czechoslovakian team. By 1962, she fought for the all-around title at the World Championships, held off only by Larissa Latyina.
Čáslavská was at her peak at the 1964 Summer Olympics in Tokyo, clearly winning the overall title and taking gold medals in the balance beam and the horse vault as well, in addition to another silver medal in the team event. She would finally win a team gold at the 1966 World Championships, breaking the Soviet monopoly in that event.
She was again dominant at the 1968 Summer Olympics, winning medals in all six events, winnning four (individual all-around, floor, uneven bars, horse vault) and finishing twice second (team all-around and balance beam). Her use of the "Mexican Hat Dance" as the music for her floor routine made her immensly popular with the Mexican crowd. Shortly after the competitions had ended, Čáslavská married with Josef Odložil, winner of the 1500 m Olympic silver medal in 1964.
For her consistent support of the Czechoslovak democratization movement (the so-called "Prague Spring") in 1968, and during the purges which followed the Soviet-led invasion in August 1968, she was deprived of the right to travel abroad and participate in public sport events both in Czechoslovakia and abroad. She was considered a "persona non grata" for many years in her home country.
After the fall of Communism in November 1989 she was rehabilitated. She became President Havel's adviser and Honorary President of the Czech-Japan Association. Later, after leaving the President's Office, she was elected President of the Czech OC.In 1995 she was appointed an IOC member. Being a member of the Women's International Hall of Fame, she was introduced in 1968 also to the International Gymnastics Hall of Fame.