In 1987, he founded the Irish Voice newspaper, the first successful Irish newspaper in New York since 1928.
In 1991, he was a founder of the Irish Americans for Clinton campaign, supporting candidate Bill Clinton for president. He led an Irish American peace delegation to Northern Ireland after Clinton was elected and he acted as intermediary between Sinn Féin and the White House at a critical period in the peace process. He played a key role in securing a U.S. visa for Gerry Adams in February 1994. His role was featured in the book Daring Diplomacy by Irish Times journalist Conor O'Clery and also in an Irish Television/PBS documentary entitled An Irish Voice.
In 2002, his book Fire in the Morning, about the Irish at the World Trade Center on September 11 attacks, reached number 2 on the Irish best seller list. O'Dowd was awarded an honorary doctorate by his alma mater University College Dublin in 2004.
He was one of the founders of the Irish Lobby for Immigration Reform in 2005, set up to lobby the Congress for comprehensive immigration reform.
O'Dowd was featured on the "People You Should Know" segment of the Paula Zahn Now program on CNN in 2007.In January 2008, he was appointed an adjunct professor at Columbia University Graduate School of Journalism.