Hillary Clinton, the former secretary of state and first lady who lost the White House to Donald J. Trump in 2016, said officially on Monday what has been unofficially clear for months: She is not running for president again in 2020.

“I’m not running,” Mrs. Clinton told a New York City television station, News 12. “But I’m going to keep on working and speaking and standing up for what I believe.”

Mrs. Clinton, the first woman to win a major-party nomination for president, remains a complicated figure for the Democratic Party as both a trailblazing female leader and also the candidate who was defeated by Mr. Trump.

Ahead of the 2020 election, she has been holding private meetings with many of the current and potential presidential candidates, including Senator Kamala Harris and former Vice President Joseph R. Biden Jr., as they sought counsel from her even before she formally ruled out another run.