A Protestant born in England and educated at Winchester College and Stanbridge Earls School, Stephenson moved to Northern Ireland, where he studied History and Politics at Queen's University Belfast. He joined the Social Democratic and Labour Party (SDLP) in the early 1980s, and became its first official press officer.
Stephenson was elected to Belfast City Council at the Northern Ireland local elections, 1993, representing the SDLP in the Castle area. He also became Deputy Chairperson of the SDLP, serving from 1995 to 1998.
In 1995, he became the party's Chairperson, serving until 1998. At the Northern Ireland Forum election in 1996, he did not stand in a constituency, but was elected as one of two regional list candidates for the SDLP, but he lost his council seat in 1997.
- "Alasdair McDonnell pays tribute to ex-chairman Jonathan Stephenson", BBC News, 23 December 2011
- Belfast City Council Elections 1993-2005, Northern Ireland Elections
- Politics 97: Social Democratic and Labour Party, BBC
- Political Leaders: Northern Ireland Archived 26 September 2008 at the Wayback Machine.
- The 1996 Forum Elections and the Peace Process, Northern Ireland Elections
|Northern Ireland Forum|
1996 - 1998
|Party political offices|
|Chairperson of the Social Democratic and Labour Party