Is an editor at Bloomberg News, where he has worked since 2013 as part of the Bloomberg Explainsteam. Prior to that, he was an editor at The New York Times, where he worked on the metro, Washington, culture and special sections desks before taking on explanatory projects for the Times website. While at the Times, he wrote over 800 bylined pieces, mainly on health and education. In 2004, his essay about his middle son’s autism was the capstone of a series the paper nominated for a Pulitzer Prize for Explanatory Reporting. In 2023, O’Neil taught a course on explanatory journalism for the Knight Center for the Americas.

O’Neil graduated from Yale University with a degree in history in 1979; his first reporting was done for the Associated Press in Nigeria and Ghana. He lives in Brooklyn with a dog and cat. O’Neil is writing lyrics for a set of new songs with members of the Cucumbers, a New Jersey indie band. An earlier collaboration with them led to an album of songs about autism that were recorded by Jackson Browne, Dar Williams and Jonatha Brooke, among others. O’Neil is also working on a graphic novel about Niccolo Machiavelli.