Speaking from her Miami Lakes campaign headquarters, Reno conceded the nomination Tuesday, saying she told Tampa lawyer Bill McBride "he was going to be a great governor.
"Bill McBride is the Democratic nominee for governor for the state of Florida and I congratulate him," Reno told a news conference.
"I want to do everything that I possibly can to see that he gets elected," Reno said. "I think Bill can lead us. I think Bill can build an educational system that we can be proud of. I look forward to working with him on issues such as prescription drugs."
Reno said she will now spend her time pushing for election reform, so voters in November will have "a just, fair, timely and accurate election. The current governor of Florida has had two shots at it now and has not met either opportunity."
McBride's wife Alex Sink was at the Cactus Club restaurant in downtown Tampa when Reno's speech came on television. Everyone at the bar clapped when the program ended.
"What a gracious person," Sink said as she watched Reno. "She's a wonderful person and a great public servant."
Unofficial totals showed that McBride had 602,346 votes, or 44.38 percent; Reno had 597,552, or 44.03 percent; and state Sen. Daryl Jones of Miami had 157,104, or 11.57 percent.
Reno gained a net total of 3,400 votes in final counts released Tuesday by Miami-Dade, Broward and other counties, not enough to erase the 8,196-vote margin McBride held after last week's preliminary tally.
McBride, a first-time candidate, emerged from the primary as the top vote-getter, but the race was marred by ballot glitches that brought back memories of the 2000 presidential election. He will face Republican Gov. Jeb Bush in November.
Unlike in 2000, when President Bush narrowly defeated Al Gore, a recount will not occur this time as McBride's lead in last week's preliminary total was larger than the half-a-percentage point margin necessary to trigger an automatic statewide recount.
Reno's lawyers have said they will not sue to force a recount or otherwise challenge the results.
Bush said he was "delighted" that it appeared his Democratic opponent has been finally decided.
"For a year there have been three opponents that have been banging on my head and saying ugly things about me, not being very specific about what they would do differently," Bush said. "Now there will be one, and I'm looking forward to it ... I look forward to a good, tough fight and I intend to win."
Reno campaign manager Mo Elleithee said that Reno has received calls from more than 600 people that will help build a case detailing numerous primary day foul-ups. There have been complaints about polls opening several hours late, polls closing early and voters being sent to the wrong precincts.
Democrats have accused Bush of failing to show leadership on the election problems. Bush has insisted that the problems were caused by Broward and Miami-Dade election officials.
"I'm confident that 65 of the 67 counties that got it right in September will get it right in November, and we're going to demand that the two counties that didn't get it right do so," Bush said Tuesday.
Meanwhile, McBride said he was close to picking a running mate.
He said he's listed more than a dozen potential lieutenant governor candidates. He declined to give names, but said, "I've almost made my mind up."