O'Brien began contributing articles to Henry Hetherington's "Poor Man's Guardian". He signed these articles with the pseudonym 'Bronterre' and James O'Brien eventually adopted it as his middle name. He worked very closely with Hetherington and when he was imprisoned for publishing an unstamped newspaper, O'Brien took over the editorship of "The Poor Man's Guardian". O'Brien and Hetherington also collaborated on other unstamped newspapers such as "The Destructive" and the "London Dispatch". In 1837 O'Brien began publishing "Bronterre's National Reformer". In an attempt to avoid paying stamp duty, the journal included essays rather than 'news items'. During this period, Henry Hetherington and O'Brien led the struggle against the stamp duty and were consistent in their arguments that working people needed cheap newspapers that contained political information.