According to the Daily Mail, the couple are hoping to find a quiet countryside location and recently visited Vaudelnay in the Loire Valley - the home of Law's mother and father - to hold talks about the idea.
A source told the newspaper: "Sienna took her wedding file with her, which is filled with all her plans, to discuss everything in detail with Jude's parents Peter and Maggie.
"After all this time and such a long and rocky history together, they want a low-key wedding. Jude and his parents really want the wedding to be held in the French countryside, so that is what is being discussed at the moment. Jude and Sienna just want to be married and start their life together."
News of the pair's engagement first emerged in April following their reunion last October.
Earlier this year, Miller confirmed that she was feeling "so happy" over the relationship.