Jonathan was Chief of Staff to Tony Blair from 1997 to 2007 and the chief British government negotiator on Northern Ireland during that time in office. 

Jonathan was a British diplomat from 1979 to 1996 working on the negotiations to return Hong Kong to China in the early 1980s, the CSCE human rights talks, CDE arms control talks with the Soviet Union in the mid 1980s, and the ‘Two plus Four’’ talks on German reunification in the late 1980s.

Since leaving government Jonathan has written, Great Hatred Little Room: Negotiating Peace in Northern Ireland and The New Machiavelli: How to wield power in the modern world.

Jonathan has also participated in a number of negotiations between governments and insurgent groups in Europe and Asia working closely with Martin Griffiths at the Centre for Humanitarian Dialogue.