Ignatiev was the co-founder of the New Abolitionist Society and co-editor of the journal Race Traitor, which promoted the idea that "treason to whiteness is loyalty to humanity".

[3] In 1995 he published the book, How the Irish Became White, an examination of the choices made by early Irish Immigrants to the United States, many of whom, when faced with xenophobia and a history of being oppressed themselves, proceeded to take the opportunity to increase their power in society by identifying as "white" and participating in oppressing darker-skinned peoples.

[citation needed] For twenty years, Ignatiev worked in a Gary, Indiana steel mill and also in the manufacturing of farming equipment and electrical components.

In 1984, he was laid off from the steel mill, approximately a year after an arrest on charges of attacking a strike-breaker's car with a paint bomb.

His dissertation, published by Routledge as the book How the Irish Became White, was advised by prominent social historian of American race and ethnicity Stephan Thernstrom and by Alan Heimert.

Ignatiev's book on Irish immigrants has been criticized for "conflat[ing] race and economic position" and for ignoring data that contradicts his theses.

[citation needed] Ignatiev's web site and publication Race Traitor displayed the motto "treason to whiteness is loyalty to humanity".

[3] Some critics, particularly David Horowitz, saw the excerpt as an example of institutional racism against white people at Harvard, in progressive culture, and in academia.

In early 1992, Ignatiev objected to the university's purchase of a toaster oven for the Dunster House dining hall that would be designated for kosher use only.

[14] Dunster House subsequently declined to renew Ignatiev's contract, saying that his conduct during the dispute was "unbecoming of a Harvard tutor".

Dunster co-master Hetty Liem said it was the job of a tutor "to foster a sense of community and tolerance and to serve as a role model for the students" and that Ignatiev had not done so.

[16] Subsequently, the encyclopedia's publisher Gale announced the appointment of an independent committee to investigate "the factual accuracy, scholarly basis, coverage, scope, and balance of every article".

[19] Ignatiev spoke at a bar in Brooklyn, New York, on October 27, 2019, at the launch party for an issue of the journal Hard Crackers, which he edited.