How can I convince my religious parents to accept my gf from a different religion?

I’m in a bit of a tough situation and could use some advice. I have been dating my girlfriend for over 3 years now, and we’re really happy together. The problem is that my parents, especially my mom, are very religious and have always been strict about my wife sharing the same religion. I’m not a religious person, but they refuse to accept our relationship or allow us to get married because they say it’s disrespectful.
Has anyone been in a similar situation? How did you handle it, and what steps did you take to get your parents to accept your relationship? Any advice would be really appreciated.