Hillary Clinton has admitted that she should have used government email as secretary of state and acknowledged she had destroyed tens of thousands of emails in her private account that she described as personal in nature.
Her email practices have raised questions about whether she fully complied with federal laws requiring government officials to preserve written communications involving official business.
Republicans have said Mrs Clinton avoided transparency and committed an ethical lapse.
The controversy has upended her careful blueprint for the rollout of her 2016 presidential campaign.
The clear front-runner for the Democratic nomination, Mrs Clinton had planned to spend March touting her work on women’s issues and giving a handful of paid speeches before announcing her candidacy in early April.
She tried to stick to that plan but as criticism from Republicans mounted and Democratic allies started publicly pushing her to address the matter, her team hastily arranged Tuesday’s brief news conference.
“I fully complied by every rule I was governed by,” Mrs Clinton said in a 20-minute news conference that marked her first comments on the matter.
The former secretary of state described her decision to rely exclusively on her private account as a matter of convenience and a way to avoid carrying two devices. She said she had not used her personal email to discuss any classified information.
“Looking back, it would have been better to use two separate phones and two separate email accounts,” she said.
Mrs Clinton said her server would remain private. She said she had exchanged 60,000 emails, half of which were personal and were discarded.
“I had no reason to save them,” Mrs Clinton said of the personal emails.
She described the destroyed communications as ones related to her daughter’s wedding, her mother’s funeral, her yoga routine and other matters.
“Everything that would be in any way connected to work is now in possession in the State Department,” Mrs Clinton said.
She broke her silence shortly after delivering remarks at a women’s empowerment event at the United Nations.
She then made her way to a nearby hallway where dozens of reporters and photographers were awaiting her first formal news conference since leaving the State Department in early 2013.
Before the question-and-answer session, Mrs Clinton’s only comment on the matter had been a late-night tweet last week saying she wanted the State Department to release her emails.
She served as the nation’s top diplomat throughout President Barack Obama’s first term. In late 2014, nearly two years after she left the administration, she turned over 55,000 pages of emails to the State Department in response to an agency request.
The department says it will take several months to review the material. Spokeswoman Jen Psaki said that once the review is complete, the emails will be posted online for the public to see.
Passages revealing anything from trade secrets to sensitive national security information could be redacted, in keeping with Freedom of Information Act guidelines.