The publicity-shy Edinburgh author said: "I just wanted to be able to get married to Neil without any rubbish happening." She declined to reveal what the disguise was.
Rowling, who gave £1m to Labour in 2008, also confirmed that she is opposed to independence for Scotland, saying "I'm pro-Union."
She made her comments in an interview prior to the publication of her first book for adults, A Casual Vacancy, on Thursday. The novel, which remains veiled in secrecy, deals with class and snobbery in a fictitious West Country village.
It is predicted to become the bestselling fiction title of the year.
Rowling said she was proud of it, adding: "The worst that can happen is that everyone says 'Well, that was dreadful, she should have stuck to writing for kids', and I can take that."