The former Mexico City mayor will face off against Xóchitl Gálvez, who is leading the opposition coalition.
Sheinbaum, a 61-year-old trained scientist, is a close ally of leftist President Andrés Manuel López Obrador.
Sheinbaum beat five other contenders to win each of five polls, averaging about 39% of the vote, the Morena party announced.
A student leader in the 1980s, Sheinbaum served as Mexico City’s environment secretary when López Obrador was mayor from 2000 to 2005.
She later served as Mexico City Mayor herself from 2018 until earlier this year, when she stepped down to run for president.
Current polling shows Sheinbaum as the front-runner, partly down to López Obrador, enjoying an approval rating of more than 60%. He is required by the constitution to leave office after a single six-year term.
But Gálvez, an outspoken female senator with indigenous roots, will be attempting to stop her.
The opposition candidate wears indigenous clothing, uses colloquial language, and is often seen cycling around Mexico City. She is seen as having a quick wit and down-to-earth demeanour that prove popular with many working-class and young Mexicans.
She has repeatedly clashed with the president over issues, including the high levels of violence in Mexico, stating that “ovaries are needed” to confront organised crime. He has accused her of being the candidate of the rich, the oligarchs,” and the “conservatives.”
Hours before Sheinbaum’s nomination was announced, her closest rival, former Foreign Minister Marcelo Ebrard, said the vote had been tainted by irregularities and called for a rerun.
But party leaders were quick to defend the process.
(Editor: Ifeanyi Mark)