O'Reilly will lead the newly created policy team at Book Aid, a charity that fights poverty in the developing world by creating learning opportunities for the poor.
He joins from the International HIV/Aids Alliance, where he was senior policy adviser. He previously worked as policy and campaigns director for the National Aids Trust in the UK and as a consultant for Amnesty International and Oxfam.
O'Reilly said: "I've seen first hand the vital role that access to information plays in tackling HIV/Aids and in protecting human rights in the developing world. Lack of information stifles development."