His work while at the Baltimore Sun landed him on the White House "Enemies List" compiled by the staff of President Richard Nixon.
He became, successively, a national political writer (starting with covering the Al Smith presidential campaign in 1928), the Sun's correspondent in London at the height of World War II, a foreign correspondent who made studies of postwar conditions in Greece, France and the Low Countries.
O'Neill covered at least 16 national political conventions up through those that nominated Hubert Humphrey and Nixon in 1968, with the exception of the years he worked abroad.
For almost 20 years, starting in 1953, he wrote a column, "Politics and People," that appeared in the morning Sun and was syndicated to many other papers.
The "Sun" marked his passing with an editorial that observed, "his standards of public morality were so high that not many could measure up to them.