The former moderator of "The View" joined the "Today" show after Katie Couric left to anchor the CBS Evening News.
Couric recently confirmed she is leaving CBS. The network said last week she will be replaced by "60 Minutes" reporter Scott Pelley.
Both Vieira's and Couric's contracts expire in June.
Longtime "Today" news anchor Ann Curry will replace Vieira, while Natalie Morales has been named news anchor and Savannah Guthrie will serve as co-host of the third hour of "Today."
"This is a difficult day for me. I'm trying hard to hold it together," People.com said Vieira announced on Monday's edition of "Today."
Vieira said she was leaving "Today" to spend more time with her three children and husband, television journalist Richard M. Cohen, who has multiple sclerosis.
Although the network confirmed her last day on the show will be in June, it said she will continue in a new role at NBC News, with an official announcement to be made in the coming months.
"Meredith is a remarkable woman and broadcaster who in five short years has left an indelible imprint on morning television," NBC News President Steve Capus said in a statement Monday. "While we will miss waking up with her each morning, we are working together on developing her next chapter at NBC News. As Meredith turns the page, we are so very fortunate to welcome Ann as co-anchor."