Being overweight decreases the lifespan.
It is well known that exceeding the usual weight range is associated with various health problems. Given that many of them can be life-threatening, weight gain is not directly responsible for reducing the life expectancy of people with illnesses. There is considerable evidence that being above the average weight could reduce living time.
For instance, a study of more than a few thousand overweight people increases the risk of dying due to a typical cause for a man between forty and forty-five years of age compared to a male who is around six years younger. The risk for a similar older woman is higher than for women six and a half years older. Another study, this time involving over a million adults, confirmed an increased risk of death due to some reason and cancer and heart disease as well as a higher percentage of moderate to severe overweight for women and men in all age groups. 
The consensus seems to be that the risk of dying is relatively straight when the BMI exceeds twenty-five and a steeper curve beyond thirty. Excess abdominal weight (central weight distribution) is another reason when BMI is relatively high. For example, when you carry a lot of your fat around your middle, but your BMI is not too high, the risk of sudden death increases.
There are also additional problems when you have other risk problems, which may lead to premature death and overweight, resulting in instant high blood pressure, high cholesterol, and smoking or diabetes. If you do not exercise, you may also have a shorter lifespan. 
However, there are always occasions when research will appear and try to find evidence that contradicts the vast majority of research. A study of men found that it is fitness, not weight, that matters in prolonging your life. According to the survey, slender and fit men are likelier to live longer than fat and healthy men. A different study showed that people who are just a little larger than the average weight are less likely to die compared to people of average weight or who are too thin. In addition, a different study found that those who eat a balanced diet live longer than those who are overweight. 
My best advice is to maintain a moderate weight, eat a balanced and healthy diet, and do enough exercise to live a long and healthy life.