Simpson originally began his journalistic career for a series of Northern Irish newspapers – The News Letter, The Irish News, and The Belfast Telegraph – after graduating in 1988 from Queens University Belfast with a degree in History and Politics. He joined the BBC in 1998 as a political correspondent. He was nominated as Television News Broadcaster of the Year at the BT UK Regional Press and Broadcast Awards 2000. In 2005 he moved to Leeds, England to the position of North of England Correspondent, where he reported for the national BBC News, including Shannon Matthews' disappearance and later discovery.
In 2008, he then returned to Belfast where he attained the position of Ireland Correspondent, taking over from Denis Murray.