The measure, which goes to the governor for signature, is a compromise reached this week by legislators after an earlier version sought to ban marriage for anyone under 18.
The Florida governor intends to sign the bill into law, a spokeswoman said.
Child marriage is legal across the United States. While 18 is typically the minimum age, every state has legal loopholes or exceptions allowing children to wed at a younger age.
Under the new Florida measure, children aged 17 can marry with parental consent but face requirements such as a premarital preparation course. Also, 17-year-olds cannot marry someone more than two years older.
"I'm very happy, even though it's not at the top line of 18. I can deal with the line of 17 with all of the requirements," said Sherry Johnson, a former child bride who had helped promote the measure.
"It eliminates just getting married," Johnson told the Thomson Reuters Foundation. "You have to show responsibility to get married."
Johnson was married at 11 to a 20-year-old man, and they had six children. Now 58, she has written a book "Forgiving the Unforgivable" and campaigns against child marriage.
Fraidy Reiss, another campaigner against child marriage, said she was disappointed the stricter version failed to win approval.
The final version leaves girls of 17 unprotected, she said. Parental consent is not a safeguard as children often are forced into marriage by their parents, she said.
"The bill that was pending would have ended child marriage. The bill as is would limit child marriage," she told the Foundation.
"It's a step in the right direction, but it's certainly not a victory."
The Florida bill is among the strictest in the nation, although some states including New York have tougher laws, Reiss said. New York requires a judge's consent for 17-year-olds to marry.
Florida's current law allows children as young as 16 to marry with parental consent and allows judges to permit marriages for younger children in cases of pregnancy.
Between 2000 and 2010, about 170,000 children under 18 were wed in 38 U.S. states where data was available, according to Unchained at Last, a non-profit group set up by Reiss.
Worldwide, the proportion of women married as children has dropped to one in five from one in four in the last decade, the United Nations' children's agency reported this week.
Children married young tend to leave school early and are at increased risk of abuse. They have more health issues in pregnancy and childbirth, and are poorer than those who marry at a later age, experts say.