Fox was engaged to Brian Austin Green, actor of Beverly Hills, 90210 and Terminator: The Sarah Connor Chronicles.

Fox has nine tattoos, which she says she gets when she has "a feeling about anything". They include a poem on her ribcage, a symbol for strength on her neck, her ex-boyfriend Brian's name on her hip and a picture of Marilyn Monroe's face on her right arm. Megan has said that Marilyn reminds her of how "Hollywood can chew you up and spit you out" Megan has mentioned she would also like to get some sort of design done by friend and well-known tattoo artist Kat Von D with the words "Tiger,Tiger Burning Bright" from poet William Blake. She also has one on her right shoulder that says "We will all laugh at gilded butterflies," a line from Shakespeare's play King Lear.

Fox has stated she has tried illegal drugs, but says "that's how I know I don't like them," additionally saying she is one of few in Hollywood not using them.