The decision to hand over the server, as well as a thumb drive of all her work-related emails to the Justice Department, represents an effort to blunt an expanding probe into her use of a private email account.
Clinton, now the Democratic presidential front-runner, "directed her team to give her email server that was used during her tenure as (secretary of state) to the Department of Justice, as well as a thumb drive containing copies of her emails already provided to the State Department," her spokesman, Nick Merrill, told CNN early Tuesday evening. "She pledged to cooperate with the government's security inquiry, and if there are more questions, we will continue to address them."
Merrill said in the meantime, Clinton's team "has worked with the State Department to ensure her emails are stored in a safe and secure manner."
The FBI, which is handling the matter, declined to comment Tuesday evening. David E. Kendall, Clinton's lawyer, did not immediately return messages seeking comment.
A senior Clinton campaign aide said the server hadn't yet changed hands as of Tuesday evening and Clinton's team is working with the Justice Department to arrange the logistics of the handover. The thumb drive, meanwhile, has been turned over. And Kendall, the aide said, has followed State Department guidance on safekeeping.
Clinton's campaign believes there are no emails from her State Department tenure on the server, since it was wiped clean after she turned over her work-related emails to the State Department, the aide said.
The aide said it's the Clinton campaign's understanding that the Justice Department isn't looking to reconstruct the server's history, but is instead concerned about the security of the emails today, since some are now classified, though they weren't classified or labeled as such at the time.
Boehner: 'It's about time'
For Clinton, the move -- which Republicans like House Speaker John Boehner have urged for months -- indicates her campaign sees a growing risk in the issue of her use of a private email server, which has stoked concerns about her trustworthiness.
"It's about time," Boehner said in a statement Tuesday night.
Since news broke in March of her use of a personal email address on a server kept in her Chappaqua, New York, home, Clinton has insisted that she's turned over all of her work-related emails to the State Department and deleted all others -- but wouldn't turn over her server to the government.
Clinton has been dogged by poll numbers showing that more Americans, by a margin of about 20 percentage points, say she's not trustworthy rather than trustworthy. A late July CNN/ORC poll found that 58% of all registered voters say it is extremely important that the next president be honest and trustworthy.
Rep. Trey Gowdy, who chairs the House Select Committee on Benghazi and has pushed for Clinton's emails for months, claimed credit for her decision to turn over the server.
"The revelation that Secretary Clinton exclusively used private email for official public business, and the multitude of issues that emanated from her decision, including this most recent one, demonstrates what can happen when Congress and those equally committed to exposing the truth, doggedly pursue facts and follow them," he said in a statement.
Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, said Clinton waited "a long time" before turning the server over.
"That's a long time for top secret classified information to be held by an unauthorized person outside of an approved, secure government facility," he said in a statement. "I look forward to the FBI answering my questions so the American people can be assured that everything has been done to protect our national security interests and hold accountable anyone who broke the rules."
Still, it's clear the GOP won't stop hitting Clinton on the campaign trail, accusing her of secrecy over her decision to wait five months to turn over the server.
Republican National Committee Chairman Reince Priebus said in a statement Tuesday night that releasing the server does little to answer questions about Clinton's honesty.
"If Hillary Clinton believed in honesty and transparency, she would have turned over her secret server months ago to an independent arbiter, not as a last resort and to the Obama Justice Department," he said. "Of course, if she really cares about transparency, she would never have had a secret server in the first place."
Clinton's decision to hand over the server comes as the intelligence community's inspector general now says at least five emails stored on Clinton's server contained classified information. The documents were from a "limited sampling" of her emails and among those 40 reviewed, said the inspector general, Charles McCullough III.
On Tuesday, McCullough sent four of the emails to chairs of several congressional committees. In a cover letter, he said two of the four emails included information that has now been classified up to top secret.
One of the five emails has since been declassified because it was no longer time-sensitive. The intelligence community maintains the remaining two contained classified material, but is deferring to the State Department on whether they should be identified as such.
McCullough said in the past that "none of the emails we reviewed had classification or dissemination markings," but that some "should have been handled as classified, appropriately marked, and transmitted via a secure network." The State Department has told McCullough that "there are potentially hundreds of classified emails within the approximately 30,000 provided by former Secretary Clinton."
Republicans shared exclusively with CNN Tuesday a review of those emails that the State Department had released, which they said showed Clinton and her aides sent information that would later be classified to six people's private email addresses. They include former Deputy Secretary of State Bill Burns; Cheryl Mills, who was Clinton's chief of staff at the State Department; and Jake Sullivan, who served as Clinton's top foreign policy adviser. Clinton also emailed information that would later be classified to close confidant Sidney Blumenthal, whose communications with Clinton about Libya have become a focus of the House committee investigating the 2012 Benghazi attacks.
"The fact that classified information was sent to and from Hillary Clinton to at least six separate individuals and potentially many more demonstrates just how big of a risk her decision to use a secret server poses to our national security," Republican National Committee research director Raj Shah told CNN.
The probe into Clinton's email practices has now expanded to include some of her top aides as part of a larger investigation on the use of private email accounts by previous secretaries of state. The Republican chairmen of three Senate committees -- intelligence, homeland security and foreign relations -- sent a joint request in March for both inspectors general to investigate the personal emails of Clinton's aides.
"We will follow the facts wherever they lead, to include former aides and associates, as appropriate," said Douglas Welty, a spokesman for the State Department's inspector general.
In a July 17 letter to the State Department, Steve A. Linick, the State Department inspector general, said his office is reviewing "the use of personal communications hardware and software by five secretaries of state and their immediate staffs." The Office of the Intelligence Community Inspector General is assisting in the review.
One of the emails containing since-classified information was released to the public, prompting the intelligence community to ask the FBI to investigate the possible compromise of classified material. The State Department now has a team of analysts from the intelligence community to review Clinton's emails before any more are released to the public.
Of the two top-secret emails sent to Congress on Tuesday, State Department spokesman John Kirby said they have not been released to the public and the department is "taking steps to ensure the information is protected and stored appropriately" while the determination was made.
"Department employees circulated these emails on unclassified systems in 2009 and 2011, and ultimately some were forwarded to Secretary Clinton," Kirby said. "They were not marked as classified."