Niall Campbell Ferguson FRSE is a Scottish–American historian who is the Milbank Family Senior Fellow at the Hoover Institution and a senior fellow at the Belfer Center for Science and International Affairs at Harvard University. Previously, he was a professor at Harvard University, the London School of Economics, New York University, a visiting professor at the New College of the Humanities, and a senior research fellow at Jesus College, Oxford.

Ferguson was born in Glasgow, Scotland, on 18 April 1964 to James Campbell Ferguson, a doctor, and Molly Archibald Hamilton, a physics teacher. Ferguson grew up in the Ibrox area of Glasgow in a home close to the Ibrox Park football stadium. He attended The Glasgow Academy. He was brought up as—and remains (as of the last version of this article) —an atheist, though he has encouraged his children to study religion and attends church occasionally.

Ferguson got to know journalist Sue Douglas in 1987, when she was his editor at The Sunday Times. They married in 1994, and went on to have three children.

In February 2010, Ferguson separated from Douglas, and thereafter started dating Ayaan Hirsi Ali. Ferguson and Douglas divorced in 2011. Ferguson married Hirsi Ali on 10 September 2011; she gave birth to their son three months later. Upset about the media coverage of his relationship with Ali, which implied that he had begun dating her before his first marriage had unraveled, Ferguson stated, "No, I never read their shitty coverage of people's private lives. I don't care about the sex lives of celebrities, so I was a little unprepared for having my private life all over the country. So yeah, I was naive, yeah."