Here’s one way: “Congratulations on your [recent] graduation and your upcoming marriage!” You could also add something like: “I wish you the greatest happiness as you move forward in this new phase in your life.”

The simplest and most neutral way is simply: "Congratulations on your graduation (and/or wedding)". You could add something else such as "best wishes for the future".

Congratulations on your graduation, and all the best on the occasion of your wedding.