"While 'Longbourn' brings to life a different side of the world Austen first created, I was impressed even more by the way this novel stands as a transporting, fully realized work of fiction in its own right," Diane Coglianese, an editor at publisher Alfred K Knopf, said in a statement.
Baker describes the chaos downstairs among the Bennets' servants, the preparation for the lavish balls, the housekeeper's thoughts about the family patriarch and the tragedy of the Napoleonic wars.
Baker, who was born and lives in Lancashire, England, has written other books, including "Offcomer," and "The Mermaid's Child."
Random House Studio and Focus Features have purchased the film rights for "Longbourn." Transworld will publish the book in Britain and Random House is the Canadian publisher.