"Exciting news ... sad 2 leave Beast but change is good," Brown posted on Twitter.
Separately, Brown issued a news release saying she is launching Tina Brown Live Media. The company will host "flash debates" and summits, including the Women in the World conference, which she launched in 2010.
A spokeswoman for IAC/InterActiveCorp, which owns The Daily Beast, declined to comment.
Brown's departure was earlier reported by Buzzfeed business editor Peter Lauria, a former Daily Beast correspondent.
The website said Brown's contract expires in January and was not going to be renewed.
Brown, the former editor of Vanity Fair and The New Yorker, presided over the end of the print run for Newsweek, which IAC bought for $1 in 2010 before merging it with the Daily Beast.
Brown said in her statement said she was proud of changes made to Newsweek, "in the battle we waged to save it from the overwhelming forces of media change."
The money-losing newsweekly magazine went online-only last year and was sold IBT Media last month.Suggest a correction