Ferguson apologised on his own blog Saturday, saying: "I should not have suggested ... that Keynes was indifferent to the long run because he had no children, nor that he had no children because he was gay.
"This was doubly stupid. First, it is obvious that people who do not have children also care about future generations. Second, I had forgotten that Keynes's wife Lydia miscarried."
Keynes, whose theories influenced government policy and macroeconomic theory, married Russian ballerina Lydia Lopokova despite being openly gay. He died in 1946.
Ferguson's apology continued: "My disagreements with Keynes's economic philosophy have never had anything to do with his sexual orientation.
"It is simply false to suggest, as I did, that his approach to economic policy was inspired by any aspect of his personal life. As those who know me and my work are well aware, I detest all prejudice, sexual or otherwise.
"My colleagues, students, and friends - straight and gay - have every right to be disappointed in me, as I am in myself. To them, and to everyone who heard my remarks ...or has read them since, I deeply and unreservedly apologise."
As well as being a history professor at Harvard, Ferguson also holds post as the Hoover Institution, Stanford University, and is a senior research fellow at Jesus College, Oxford.
- AAP