During the 1960s Clarke won 9 Australian championships and 12 Victorian track championships ranging from 1500 m to 6 miles (9.7 km).

He won the bronze medal in the 10,000 metre (m) race at the 1964 Summer Olympics when he was upset by Billy Mills, and never won an Olympic gold medal.
However, Emil Zatopek gave him one of his own Gold medals, which Clarke described as one of his most cherished presents.
At the 1968 Summer Olympics in Mexico City, Clarke collapsed and nearly died from altitude sickness sustained during the gruelling 10,000 m race final.
 Despite training in the Alps to get acclimatised to high altitudes at Mexico City, this could not put him on par with many opponents from Africa, who had always run at high altitude (with the notable exception of 5,000 m gold medalist and 10,000 m bronze medalist Mohammed Gammoudi of Tunisia, who was born and lived not far above sea level).
 Clarke finished in sixth place, but remembered nothing of the last lap.
He recovered sufficiently to compete in the 5,000 metre heats a few days later.

In the 1962 British Empire and Commonwealth Games, he won silver in the 3 mile event, and in the 1966 Games he won silver medals in the 3 miles (4.8 km) and 6 miles (9.7 km) events.

During a 44-day European tour in 1965, he competed 18 times and broke 12 world records, including the 20,000 m (12.4 miles).
On 10 July, at London's White City Stadium, he became the first man to run 3 miles in under 13 minutes, lowering the world record to 12:52.4.
Four days later, in Oslo, he lowered his own 10,000 m world record by 36.2 seconds to 27:39.4, becoming the first man to break the 28 minute barrier.
During the 1960s Clarke won 9 Australian championships and 12 Victorian track championships ranging from 1500 m to 6 miles (9.7 km).
He won the bronze medal in the 10,000 metre (m) race at the 1964 Summer Olympics when he was upset by Billy Mills, and never won an Olympic gold medal. However, Emil Zatopek gave him one of his own Gold medals, which Clarke described as one of his most cherished presents. At the 1968 Summer Olympics in Mexico City, Clarke collapsed and nearly died from altitude sickness sustained during the gruelling 10,000 m race final.  Despite training in the Alps to get acclimatised to high altitudes at Mexico City, this could not put him on par with many opponents from Africa, who had always run at high altitude (with the notable exception of 5,000 m gold medalist and 10,000 m bronze medalist Mohammed Gammoudi of Tunisia, who was born and lived not far above sea level).  Clarke finished in sixth place, but remembered nothing of the last lap. He recovered sufficiently to compete in the 5,000 metre heats a few days later.
In the 1962 British Empire and Commonwealth Games, he won silver in the 3 mile event, and in the 1966 Games he won silver medals in the 3 miles (4.8 km) and 6 miles (9.7 km) events.
During a 44-day European tour in 1965, he competed 18 times and broke 12 world records, including the 20,000 m (12.4 miles). On 10 July, at London's White City Stadium, he became the first man to run 3 miles in under 13 minutes, lowering the world record to 12:52.4. Four days later, in Oslo, he lowered his own 10,000 m world record by 36.2 seconds to 27:39.4, becoming the first man to break the 28 minute barrier.
Ron Clarke