In 1967 she married Janusz Szewińsk and arrived at the 1968 Games in Mexico City as Irena Szewińska. She failed to qualify for the final in the long jump and picked up a bronze medal in the 100m. Then she overcame a slow start to win the gold medal in the 200m in world record time. After adding a bronze medal in the 200 at the 1972 Munich Games, Szewińska switched to the 400m in 1973 and the following year she became the first woman to break the 50-second barrier.
At the 1976 Olympic Games, Szewińska won the 400m with another world record to bring her career total to seven medals in five different events. Between 1974 and 1978 she won 34 straight 400m finals. In 1980 she participated in the Olympic Games in Moscow, but pulled a muscle in the semifinals of the 400 and was eliminated. Szewińska was named a member of the International Olympic Committee in 1998.