Overjoyed couples filed into courthouses and exchanged vows just after midnight, as Florida became the 36th of America's 50 states to allow gay marriage.
"I'm glad it's finally legal," William Lee Jones told the Miami Herald after he married his partner of more than 10 years, Aaron Huntsman.
The couple were among several who had sued Florida for the right to marry.
US District Judge Robert Hinkle ruled last week that court officials must not enforce the state's ban, which was approved by voters in 2008.
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So many couples showed up at the courthouses in some counties that officials held mass wedding ceremonies as jubilant friends and supporters cheered outside.
"It's about time, is what I feel. I didn't think it would happen in my lifetime," Irma Oliver of West Palm Beach told the Palm Beach Post as she married her partner of a decade, Julia Borghese.
Florida is America's third most populous state behind California and Texas, with a population of about 20 million.
This cleared the way for married gay and lesbian couples to enjoy the same rights and privileges under federal law as their straight counterparts.
It nevertheless left it to each of the 50 states to legalise or ban same-sex marriages.