Daniel O'Neill immigrated to the United States from Ireland in 1851, settling in Pittsburgh, Pennsylvania.

[citation needed] O'Neill's interest in journalism began at an early age and he was a contributor to the Wexford Independent.

Perhaps his impact at the paper can be summed up by comments which appeared at the time of his death; In addition to his activities with the newspaper, O'Neill served several terms in the Pittsburgh City Council and was a member of the Electoral College of Pennsylvania.

Shortly after his death, Daniel's wife Emma married his brother Eugene M. O'Neill.

At O'Neill's gravesite is a memorial statue showing him sitting at an editor's desk honoring his long career as a Pittsburgh newspaperman.