Risk level was compared with that of people working a typical 35 to 40-hour week.
Working 41 to 48 hours a week was associated with a 10% risk increase, which rose higher as the hours mounted up. Working 49 to 54 hours pushed up the chances of a stroke by 27% and 55 or more hours raised the risk by a third.
The hardest grafters also experienced a more modest 13% increased risk of heart disease.
Scientists employed a meta-analysis technique to pull together results from 25 studies allowing trends to be seen that may have been previously hidden.
Lead author Professor Mika Kivimaki, from University College London, said: "Health professionals should be aware that working long hours is associated with a significantly increased risk of stroke, and perhaps also coronary heart disease."
About 150,000 people in the UK suffer a stroke each year, according to official statistics.
Dr Shanim Quadir of The Stroke Association said: "Working long hours involves sitting for long periods, experiencing stress, and leads to less time to look after yourself."
