The chairman said he would retire "in the coming weeks," in an announcement that was expected, although the timing of his departure was not previously known, The New York Times reported Friday.
Consumer advocacy organization Public Knowledge said Genachowski's tenure at the FCC was defined by "missed opportunities."
"The chairman deserves credit for defending both the commission's data roaming rules and unlicensed spectrum, for permitting DISH Network to provide terrestrial wireless service, and for releasing the staff report that helped to end AT&T's attempted takeover of T-Mobile," the organization said in a statement.
"But it remains to be seen whether those positive steps will mitigate the enormous consolidation that has taken place in the broadband marketplace under his watch," the group said.
With the recent resignation of Republican Commissioner Robert McDowell, the agency will be left with two of five board member jobs unfilled. Of the three remaining commissioners, two are Democrats.
"Over the past four years, we've focused the FCC on broadband, wired and wireless, working to drive economic growth and improve the lives of all Americans," Genachowski told staff members, the agency said in a news release.
"Today, America's broadband economy is thriving, with record-setting private investment; unparalleled innovation in networks, devices and apps; and renewed U.S. leadership around the world," the chairman said.
Former FCC Chairman Michael Powell, a Republican, said Genachowski "wisely believed that ubiquitous Internet connectivity would be the defining technology of our day ... and his leadership has ensured that America's robust wired and wireless broadband networks are world class."