London was born in San Diego, California, the son of Debbie (née Osborn), a waitress, and Frank London, a sheet metal worker. He was raised mainly in DeSoto, Texas. After divorcing Jeremy's father, his mother moved the family 13 times in six years. His identical twin brother, Jason, is older by 27 minutes and is also an actor. Jeremy has worked mostly in television while Jason has opted for a career in feature films. The two have acted alongside each other only once – in the February 3, 2003 episode of the WB's 7th Heaven, entitled "Smoking." They have also competed for the same role – Jeremy's first audition was for a part in the 1991 film The Man in the Moon, which Jason won, leaving Jeremy the part of his brother's stunt double.