Tant announced her decision Friday, three days after Democrats lost presidential and U.S. Senate races in Florida and failed to make serious dents in the Republican majorities in the Legislature.
"It has truly been a privilege and an honor to serve as your chair and I wanted you to hear from me first that I've decided to not seek reelection in January," Tant wrote in an email to party members. "I will use the remainder of my term to ensure that the next chair is able to hit the ground running on day one with as smooth of a transition as possible."
Tant, a major fund-raiser for President Barack Obama, was chosen chairwoman in January 2013.
But the party has suffered high-profile losses during the past few years, including Republican Gov. Rick Scott winning a second term in 2014 by fending off Democrat Charlie Crist. Florida Democrats went into Tuesday's elections hoping they could help put Hillary Clinton into the White House, but Republican Donald Trump won the state, helping propel him to a national victory.
For much of this year, Democratic leaders also hoped U.S. Rep. Patrick Murphy would be able to capture a key U.S. Senate seat. But incumbent Republican Marco Rubio handily beat Murphy on Tuesday.
"While this wasn't the outcome we worked so hard for, we stood for what is best in our country —- justice, equality, compassion and hope," Tant wrote in the email that was also released to the media.
Democrats on Tuesday won one major state Senate race in Miami, with Democratic state Rep. Jose Javier Rodriguez toppling incumbent Republican Miguel Diaz de la Portilla. But Democrats lost other closely watched Senate races in Miami, Tampa and the Gainesville area.
Tant's announcement came a day after she expressed in an email to party members that, "The results of the election weren't what we anticipated, and they aren't what we were hoping for."
In that email, Tant wrote that the party members would "dust themselves off, and keep fighting for the issues that we worked so hard for this election."
Florida Democratic Party Chairwoman Allison Tant will leave the job when her term expires.