Alexander, who will be 62 then, is expected to leave the main producer and manager of U.S. signals intelligence in March, NSA spokeswoman Vanee Vines said Wednesday in a statement to United Press International.
Alexander, appointed to the NSA spot in 2005 by George W. Bush administration Defense Secretary Donald Rumsfeld, "served well beyond a normal rotation, having been 'extended' three times," Vines told UPI.
The four-star general is a career Army intelligence officer who is also chief of the Defense Department's Central Security Service and commander of the military's Cyber Command.
After the disclosures by former NSA contractor Edward Snowden of mass NSA surveillance of U.S. citizens and foreign nationals, Alexander became the public face of Washington's secret collection of personal communications records in the name of national security.
He has consistently defended the controversial practice, saying it has helped prevent dozens of "potential terrorist events" since the Sept. 11, 2001, attacks.
Alexander's departure "has nothing to do with media leaks," Vines' statement to UPI said.
"The decision for his retirement was made prior" to the leaks, in an agreement made with Defense Secretary Chuck Hagel in March, she said.
Snowden started leaking information to the press in May, with the first reports published in June.
"The process for selecting his successor is ongoing," Vines told UPI.
Alexander's departure and potential successor are widely expected to prompt congressional debate over whether the huge NSA infrastructure built during Alexander's tenure will remain or be restricted.
Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., has drafted legislation to eliminate the NSA's ability to systematically obtain Americans' calling records.
Rep. Jim Sensenbrenner, R-Wis., co-author of the Patriot Act, whose secret interpretation is used to justify the mass metadata collection, is drafting a bill to cut back on domestic surveillance programs.