Katherine Archuleta will be replaced on an acting basis by Beth Cobert.
The US Office of Personnel Management (OPM) director Katherine Archuleta has resigned following a huge data breach involving over 20 million people.
Hackers in China are suspected of conducting a massive data breach in the US, compromising the personal information of millions of government employees of the OPM.
The OPM initially said over four million current and former federal employees were affected by the breach.
However, the department said last week that the data of more than 20 million people may have been affected.
The agency said sensitive data, including the social security numbers of 21.5 million individuals, was stolen from the background investigation databases. It includes 19.7 million individuals that applied for a background investigation, and 1.8 million non-applicants.
Archuleta, who led the agency for 18 months, said in a statement, "This morning, I offered, and the president accepted, my resignation as the director of the Office of Personnel Management.
"I conveyed to the president that I believe it is best for me to step aside and allow new leadership to step in, enabling the agency to move beyond the current challenges and allowing the employees at OPM to continue their important work."
Archuleta will be replaced on an acting basis by Beth Cobert, who is currently serving as deputy director of the Office of Management and Budget.