You need to know that why your parents are opposing? Try to understand their perspective and then you can put your views to them. If you do not have ease of open communication with them then you have to take help of someone who can put up your feelings to them. Most of the time parents act in best interest of their child, you only need to understand what it is, with open mind!
However, I have always said in such type of cases, if you would have known beforehand that your parents would not agree to such relationship you should have talk to them before progressing. Most of the time this type of situations end up in the mess