News of his departure came before a meeting of the powerful arts and science faculty, set for next Tuesday, which was expected to deliver a resounding vote of no confidence in his stewardship of the university.
Mr Summers' tenure had been stormy from the outset. Soon after arriving in 2001, he took aim at grade inflation, limiting the ranks of honours students and reducing the total of A and B grades awarded.
He then set about asserting his control over some of Harvard's powerful fiefdoms. That brought him into confrontation with Cornel West, the celebrated professor of African-American studies, who left Harvard for Princeton in April 2002. The clash involved two very large egos. But long before that, Mr Summers was known for his often brusque style and a disregard for political correctness.
"Larry Summers strikes me as the Ariel Sharon of American higher education," Dr West told an interviewer at the time. "He struck me very much as a bull in a china shop, and as a bully in a very delicate and dangerous situation."
Trouble flaredlast year when the Harvard president told a conference that "innate differences" may explain why there were so few women in the highest echelons of science. The result was outcry in the female academic community, grovelling apologies from Mr Summers, and the creation of task forces to examine ways of reducing barriers to the advancement of women in science.
But the last straw proved to be the departure of William Kirby, the dean of the arts and science faculty, widely seen as having been pushed out by Mr Summers. At a tense faculty meeting last month, various speakers said that campus morale was "grim".
Others accused Mr Summers of cronyism, by refusing to bring sanctions against his friend Andrei Shleifer, a leading Harvard economist. In 2004, Mr Shleifer was found by a federal court to have conspired to defraud the US government by making personal investments in Russia, in conflict with his US government consulting contract to advise Russia.
Technically, Mr Summers could only be removed by the seven-member Harvard Corporation, the university's board of directors, of which he is a member. There, support for him had seemed stronger. But he seems to have concluded that a second bruising faculty vote of no confidence would plunge Harvard into a debilitating crisis.
Oddly, Mr Summers' largest pool of support appears to have been among students. A poll by the student newspaper found that fewer than one in five undergraduates and graduates thought he should step down, while 57 per cent believed he should stay.Reuse content