McFeely was born in New York City, the son of William C. McFeely, an executive with Grand Union supermarkets, and Marguerite McFeely (née Shield), a homemaker.[2] He graduated from Ramsey High School, in New Jersey. After earning a B.A. at Amherst College in 1952, he worked for the First National City Bank of New York for eight years, before deciding to pursue graduate work in American studies at Yale University, where he received his Ph.D. in 1966.[2] At Yale, he studied with, among others, C. Vann Woodward, whose book The Strange Career of Jim Crow was a staple of the Civil Rights Movement. Like Woodward, he sought to employ history in the service of civil rights. His dissertation, later the 1968 book Yankee Stepfather, explored the ill-fated Freedmen's Bureau which was created to help ex-slaves after the Civil War.
He taught for 16 years at Mount Holyoke College before joining the University of Georgia in 1986 as the Constance E. Smith Fellow. McFeely won the 1982 Pulitzer Prize for Biography or Autobiography for his 1981 biography of Ulysses S. Grant, which portrayed the general and president in a harsh light. He concluded that Grant "did not rise above limited talents or inspire others to do so in ways that make his administration a credit to American politics."[4]
McFeely retired in 1997. He was a fellow at Harvard's Radcliffe Institute for Advanced Study during the 2006–2007 academic year, where he studied Henry Adams and his wife Clover Adams, and Clarence King and his wife Ada Copeland King.[5] He was a visiting scholar and associate member of Harvard's Afro-American Studies Department and an associate of their Humanities Center.