People with high blood pressure are almost 60% more likely to develop diabetes, according to research on 4.1 million people.
The Oxford University study provides the strongest evidence yet of a link between the two conditions.
Experts behind the study said more research was needed to see whether using drugs to lower blood pressure would help prevent people developing Type 2 diabetes.
Professor Kazem Rahimi, deputy director of the George Institute for Global Health UK at Oxford, which carried out the study, said: "This is potentially a game changer in the understanding and treatment of diabetes.
"Diabetes affects more than 400 million people worldwide and we know that diabetics are more likely to suffer from cardiovascular disease such as heart attacks, stroke and heart failure.
"We can't say for certain that one causes the other, but this study helps to connect the dots, showing that if you have high blood pressure there is a significantly greater chance of developing diabetes.
"Understanding the link will help us better communicate risks to patients and can provide another motivation for patients and doctors to aim for tight blood pressure control."
The research on UK adults was published in the Journal of the American College of Cardiology (JACC).
All the adults were free of diabetes and cardiovascular disease at the start of the study.
The result showed people were at almost 60% higher risk of diabetes if they had high blood pressure.
High blood pressure was linked with new cases of diabetes in a wide range of individuals, including men and women, people of varying ages, as well as those who were normal weight, overweight and obese.
Prof Rahimi said: "At a minimum we know for certain that the link exists, but is high blood pressure a cause of diabetes or just a risk factor? We still don't know.
"In particular researchers can now look at whether lowering blood pressure is an effective treatment or reduces the risk of getting diabetes."
Dr Richard Elliott, Diabetes UK research communications manager, said: "We already know that you are more at risk of Type 2 diabetes if you have ever had high blood pressure, a heart attack or a stroke.
"The results of this large study reinforce this link. We know that the best way to reduce your risk of Type 2 diabetes is to maintain a healthy weight by eating a healthy balanced diet and taking part in regular physical activity."