It was directed by Judd Apatow , and stars Seth Rogen and Katherine Heigl . Knocked Up is a 2007 American comedy film co-produced , written , and directed by Judd Apatow . Starring Seth Rogen , Katherine Heigl , Paul Rudd , and Leslie Mann , the film follows the repercussions of a drunken one-night stand between Rogen 's slacker character and Heigl 's just-promoted media personality that results in an unintended pregnancy .