The former Hills star wore a gorgeous cream dress, featuring a chiffon overlay with a drop hem, to the event, which was held at The Grove in Los Angeles.
Lauren, 27, also wore cream sandals, a pale pedicure and minimal jewellery, and she completed her look by sweeping her long blonde hair into a stunning high bun.
She kept her make-up natural, choosing just a pale rose lipstick and a slick of black eyeliner to open up her peepers.
Lauren has based her latest novel on her own experiences of starring in a reality show. Prior to The Hills, she also had a lead role in MTV's Laguna Beach.
Speaking about her book, which is the eighth in her 'Fame Game' series, she said: "It's the last book in the series and I get to wrap everything up.
"It's kind of bitter sweet, as it's an accomplishment because you've finished it, but it's a little bit sad to say goodbye to character that you've spent so long creating."
Have you read any of Lauren's books? Tell us below, as the best comment from across the website each week wins £50!