Day is a former Russian linguist for the U.S. Army Military Intelligence. She currently writes romantic fiction novels for New American Library (speculative/paranormal) and Kensington Brava (historical) and Zebra (futuristic - under the pseudonym Livia Dare). Day has also published fiction works with Tor-Forge (urban fantasy - under the pseudonym S. J. Day), HarperCollins Avon (speculative/paranormal), Black Lace (contemporary), Ellora's Cave (contemporary/paranormal/futuristic), and non-fiction for BenBella Books and others.
She is the co-founder of Passionate Ink, a special interest chapter of Romance Writers of America, and she has served on Romance Writers of America's Board of Directors since 2009. She had been honored with the Romantic Times Reviewers' Choice Award, the EPPIE Award, the National Readers' Choice Award, and multiple nominations for Romance Writers of America’s RITA Award. She travels extensively in conjunction with various speaking engagements. In addition to presenting workshops before writing groups around the country, she is a frequent panelist at events such as the Romantic Times Convention, Romance Writers of America's National Convention, and Comic-Con.
Day is also a member of Novelists, Inc. and Science Fiction and Fantasy Writers of America.