The move comes less than 24 hours after Steve Case, the chairman of AOL Time Warner, which owns CNN, said he would step down from his position in May, around the same time Mr. Isaacson said he would depart.
Jim Walton, president and chief operating officer of CNN, will replace Mr. Isaacson. Eason Jordan, a 20-year CNN veteran, will remain as the chief news executive.
"Walter and I have worked very closely together over the past couple of years and we worked closely together when he was at Time," Mr. Jordon said. "He's a great journalist. He brought a lot of great ideas to the table, some new thinking, and those things are enormously beneficial to CNN."
No change to strategy
Mr. Walton said he does not expect to change the current strategy at CNN. "Fundamental change, that would be changing the business. You will not see that," he said. "You will not see more of that type of thing."
"If you look at the strategy that we started with two years ago," said Jamie Kellner, chairman-CEO of Turner Broadcasting Systems, in a hastily arranged conference call, "which was to create hour-long, appointment viewing shows, similar to what ABC, NBC and CBS do, instead of rolling newscasts, that is working. ... We won't change the programs we have in the years ahead, but we will continue to add more of those.
"And we will use the people currently operating these networks, because we are achieving a lot of success right now," Mr. Kellner said. CNN's ratings have been up 20% to 30%, depending upon the daypart, during the past few seasons. So we are very happy with the performance of our executive team."
Nevertheless, under Mr. Isaacson's watch, CNN's ratings slipped behind those of News Corp.'s Fox News Channel for the first time.
In the call, Mr. Isaacson essentially endorsed the musings of his surprised former colleagues at company sibling Time Inc. who said he'd never seemed as happy at CNN as he had been at the magazine giant.
"I love the journalism at CNN," he said, but conceded that "it took me a while to get into the TV management" aspects of his job. He added that he didn't see himself "as a natural-born TV executive for the rest of my life" and that the Aspen post appealed to him because it involved "wrestling with ideas."
Mr. Isaacson, formerly the youngest managing editor -- the highest editorial position -- at Time Inc.'s flagship Time magazine, was something of a golden boy at Time Inc., where the formidable combination of his fierce intellect and ambition was legendary. He went over to head CNN in July 2001.
Roger Ailes, chairman-CEO of Fox News Channel, said, "Walter Isaacson is an excellent journalist with enormous talent who made a smooth transition from the print to the TV medium. He is a fine competitor and friend, whose knowledge of the news business raised the bar for the industry. We wish him well in the next phase of an already distinguished career."
During the conference call, Mr. Kellner reiterated comments he made the past weekend about the long-discussed potential merger of CNN and ABC News' operations, saying the companies were "not engaged" in any discussion currently and that CNN needed about six weeks to analyze "whether we think it's a good decision for us."