Dunn joined the White House in May, replacing Ellen Moran, who left abruptly to become chief of staff at the Commerce Department.
Dunn worked extensively on the Obama campaign and has been featured prominently as one of the the highest ranking women on the Obama communications and strategy team. She was part of a "60 Minutes" piece on the Obama campaign.
Officials said Dunn will remain involved in future White House communications and strategy decisions, but as an outside consultant. Dunn came to the White House from her firm, Squier, Knapp, Dunn Communiations.
Dunn was among the officials most identified with White House criticism of the Fox News Channel. Numerous White House aides said her departure, had nothing to do with her criticism of Fox.
Dunn has always carried the "interim" title and it has long been understood she would leave the White House by year's end. To the degree her departure is early, it is early by a matter of weeks.White House officials said Dunn actually stayed longer than she originally intended, in part to assist the White House in the health care debate.
Dunn is married to Robert "Bob" Bauer, a prominent Washington elections lawyer who is currently President Obama's personal attorney and chief counsel for the Democratic National Committee.
Fox News has previously reported that Bauer is the leading candidate to replace White House Counsel Greg Craig, who will leave his post by year's end.
Pfeiffer, 33, was communications director for the Obama campaign and worked out of its Chicago headquarters. He previously held communications posts with Democratic Sens. Evan Bayh of Indiana, and Tom Daschle and Tim Johnson, both of South Dakota.