Begala discussed his departure with Mr. Clinton during the president's New Hampshire trip last Thursday.
The political adviser will leave his White House job Monday to take a teaching post at Georgetown University and to return to writing a column for George magazine.
Begala said he was grateful to President Clinton for giving him a chance to play in the big leagues of politics and serve at the White House.
"But it's time to move on," he said in announcing his decision on Don Imus' radio show. "I've got a chance to do what I really love, teaching and writing."
Imus asked Begala, one of the White House officials who had to weather the Monica Lewinsky scandal, whether he would return to the administration which has often been consumed by controversy, "when the other shoe drops."
Begala quipped, "I don't know about any shoes dropping; I feel like I spent the last year in Imelda Marcos' closet. But it's behind us now, it's behind us and we're going to move on with the important business of bipartisan cooperation and so that means it's a good time for me to leave."
In a prepared statement, President Clinton calls Begala a "close and trusted adviser" and praises his "razor-sharp mind and wit."