NEW YORK - On her 15th anniversary on “Today,” Katie Couric told viewers Wednesday she's leaving to join CBS and become the first woman to solely anchor a network evening newscast.

“I wanted to tell all of you out there ... that after listening to my heart and my gut ... I've decided I'll be leaving ‘Today' at the end of May,” she said. “I really feel as if we've become friends through the years.”

The 49-year-old Couric, the longest-serving anchor in “Today” show history, is expected to replace Bob Schieffer on the third-rated CBS broadcast in September.

Following a months-long guessing game that has consumed the TV industry, Couric chose the 15th anniversary of her first day as “Today” co-host in 1991 to say that it's time for a change.

“It's been such an honor and a privilege to occupy this seat for as long as I have,” she said. “Sometimes I think change is a good thing,” Couric said. “Although it may be terrifying to get out of your comfort zone, it's also very exciting to start a new chapter in your life.”

The bold move simultaneously forces NBC to find a new team for “Today,” television's most profitable news program, and gives CBS News President Sean McManus a major success in his effort to lure more stars to his beleaguered news organization.

Meredith Vieira of the daytime chat show “The View” has emerged as the leading candidate to team with Matt Lauer at “Today.” Vieira, a former CBS News reporter who won a Daytime Emmy as host of “Who Wants to Be a Millionaire,” had previously turned down offers to return to news since joining “The View.”

Couric, Lauer, newsreader Ann Curry and weathercaster Al Roker have formed TV news' most successful morning team in history since 1997, with “Today” riding an unprecedented 10-year ratings winning streak.

During that time, morning news programs have simultaneously grown in influence and have become important entertainment vehicles. The job required Couric to both interview presidents and don goofy costumes on Halloween.

Couric's NBC contract extends to the end of May and she's expected to remain at “Today” through that ratings sweeps month.

The lure of trying something new and making history in the evening proved enticing to Couric, who is also expected to contribute to 󈬬 Minutes.” She spurned a more lucrative offer - about $20 million a year - to remain at NBC and accept CBS' bid at a salary near her current range of $13 million to $15 million, according to a non-network person close to negotiations who spoke on condition of anonymity.

With Schieffer filling in during the year since Dan Rather's exit, the “CBS Evening News” is the only network evening newscast rising in the ratings. But it's still in third place behind NBC and ABC.

“I will be delighted if she came,” Schieffer said Tuesday. “I think she'll be a great addition to a very good news team. ... I've known Katie for years and I think the world of her.”

If a deal with Vieira can't be reached, the top in-house candidates to replace Couric are “Today” weekend anchor Campbell Brown, NBC reporter Natalie Morales and Curry.

“If it comes to an end, I'll be the first to cry,” Curry told “Access Hollywood” about Couric before her colleague's announcement. “If she leaves, she'll be very hard to replace.”