Born Sybil Anne Rivers in Atlanta, Georgia, she was raised in Fairburn, Georgia, and attended Auburn University, where she was a member of the Delta Delta Delta Sorority. While at Auburn she wrote a column for the student newspaper, The Auburn Plainsman, that favored integration. The university administration attempted to suppress the column, and ultimately fired her, and the column garnered national attention. She later became a senior editor for Atlanta magazine. At the age of thirty she married Heyward Siddons, and she and her husband now live in Charleston, South Carolina, and spend summers in Maine.
Peachtree Road, set in Atlanta, was a bestselling novel described as "the Southern novel for our generation" by Pat Conroy. More than a million copies are in print. In 1989 her book Heartbreak Hotel became a movie titled Heart of Dixie, which starred Ally Sheedy, Virginia Madsen, Phoebe Cates, Treat Williams, Kyle Secor and Peter Berg.
Siddons's book The House Next Door was adapted for a made-for-television movie that aired in 2006 on Lifetime Television, starring Mark-Paul Gosselaar, Colin Ferguson, and Lara Flynn Boyle. The film tells the story of a woman who is drawn to a home filled with an evil presence that preys on its inhabitants’ weaknesses.
Siddons recently signed a three-book contract with Warner Books and has finished work on her latest novel, titled Off Season, released August 13, 2008.
Stephen King, in his non-fiction review of the horror medium, Danse Macabre, listed "The House Next Door" as one of the finest horror novels of the 20th Century, and provides a lengthy review of the novel in its "Horror Fiction" section.