Study author Michelle McDonnell, a lecturer in the School of Health Sciences at the International Centre for Allied Health Evidence, University of South Australia, said the study involved 27,000 Americans, age 45 and older who were tracked for an average of 5.7 years.
One-third of participants reported being inactive, exercising less than once a week.
The study, published in the journal Stroke, found among men, only those who exercised at moderate or vigorous intensity four or more times a week had a lowered stroke risk. Among women, the relationship between stroke and frequency of activity was less clear.
Inactive people were 20 percent more likely to experience a stroke or mini-stroke than those who exercised at moderate to vigorous intensity -- enough to break a sweat -- at least four times a week, the study said.
"The stroke-lowering benefits of physical activity are related to its impact on other risk factors," McDonnell said in a statement. "Exercise reduces blood pressure, weight and diabetes. If exercise was a pill, you'd be taking one pill to treat four or five different conditions."
Study participants were part of the Reasons for Geographic and Ethnic Differences in Stroke study -- divided relatively equally between black and white and male and female, with more people from the "Stroke Belt" states in the southeast.