Under its terms, most felons will automatically have their voting rights restored when they complete their sentences or go on probation.
Before the result, Florida was one of the four states that did not restore voting rights to felons after serving their sentences.
"'Kol hakavod' to the Reform Jewish communities in Florida - and across the US - who organized and mobilized to make this happen", the national Religious Action Center said on Twitter, using the Hebrew term for "well done".
This is the most significant expansion of voting rights in America since the 19th Amendment to the United States Constitution granted votes to women in 1920 and the passage of the Voting Rights Act of 1965. Florida Gov. Rick Scott and Rep. Ron DeSantis opposed the measure. Scott boasted in Clemency Board meetings, where he presided alongside the three state Cabinet members, that "there's absolutely no standards so we can make any decisions we want".
"For too long, Florida has been an extreme outlier", concluded ACLU of Florida executive director Howard Simon.
Florida's felony disenfranchisement laws were, like those in many other states, a vestige of the its racist 19th century "Black Codes", which attempted to systematically criminalize freed slaves following the Civil War, and then bar them from voting.
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The secretary of state also said three ongoing non-proliferation projects in Iran are exempt from sanctions . The first round of the anti-Iran bans - which had been lifted under the accord - were re-imposed in August.
"Today, Floridians from all walks of life and political persuasions came together to make Florida a better democracy and affirm our shared value that when a debt is paid, it's paid", Desmond Meade, chairman of Floridians for a Fair Democracy, a group that led efforts to pass the amendment, said in a prepared statement.
As black people are disproportionately represented among former felons, one in five black Florida voters are prohibited from voting due to a criminal record.
With 81 percent reporting on Tuesday evening, the ballot measure surpassed the 60 percent threshold needed, securing support from 64.1 percent of voters.
Florida's Senate and gubernatorial races remain too close to call, but there's already some major news out of the state.
"Right about now, we can presently say that we have made history", said Rhonda Thomas, manager of the "Let My People Vote" campaign. A disproportionate share of those arrested and incarcerated in Florida are minorities, particularly African Americans. To see so many people in a room crying, hugging each other and really just celebrating years worth of hard work.
In February, a federal judge ruled the state's policy requiring felons to petition the government to have their voting rights restored was unconstitutional because it was lengthy, arbitrary and forced them to "kow-tow" to the whims of state politicians.