There has been research concluding that green tea may have a small impact on weight loss, but not enough effect to be clinically significant.
Green tea contains caffeine, and catechins—a type of flavonoid and antioxidant—and both these compounds are able to speed up the metabolism. This may be why there is an impact on weight, as a faster metabolism means you burn more calories when you are at rest.
Regardless of whether or not green tea has inherent properties that help reduce weight loss, it does not contain calories, and you usually don’t add sugar or milk to it. This means that if you swap your usual milky and sweetened coffees or teas out for green tea, it’s possible you could see a gradual and minor impact on your weight, if weight loss is your aim.