Tim Garden was born in 1944, educated at the King's School, Worcester, and joined the Royal Air Force as a university cadet while at St Catherine's College, Oxford University reading Physics. He was a member of Oxford University Air Squadron from 1962 to 1965. He was a squadron pilot on No 3 Squadron flying Canberra light bombers in Germany before becoming a flying instructor on Jet Provosts. He has commanded a jet flying training unit, a Vulcan bomber squadron and a helicopter base.

He completed his staff training with the Army, and did a postgraduate International Relations degree at Magdalene College Cambridge. He spent three years as the Director of Defence Studies for the Royal Air Force, lecturing internationally on strategic studies. He was then appointed as station commander of RAF Odiham, where he flew Puma and Chinook helicopters. He then spent six years at the Ministry of Defence on both the air and central staffs, including a period on the Air Force Board as Assistant Chief of the Air Staff. His last MOD appointment was as Assistant Chief of the Defence Staff(Programmes) with responsibility for long term defence programme planning for all three Services. He was subsequently appointed to be Commandant of the Royal College of Defence Studies and was in post for the 1994 and 1995 courses. He retired from the RAF in 1996 as an Air Marshal, and was a Web site consultant before being appointed as Director of the Royal Institute of International Affairs at Chatham House, London. Since mid 1998, he has been writing, broadcasting, lecturing and undertaking projects for the British Government, the US Department of Defence and NATO. He was joint chief editor for The Source, an internet public management journal from 1999-2002. In 2000, he provided advice to the Palestinian Authority on negotiations with Israel under the auspices of the Adam Smith Institute. He was Distinguished Visiting Fellow and Scholar-in-Residence to Indiana University for the Spring 2001 Semester, and continues to lecture there regularly by video. He returned to Indiana in early 2004 as the Wells Professor. He has been Visiting Professor at the Centre for Defence Studies at King's College, London since 2000 engaged in research projects on improving European defence capabilities, Defence Diplomacy, interoperability for NATO forces and counter-terrorism. He appears as the military advisor on the BBC television series Crisis Command.
He became a Liberal democrat member of the House of Lords in June 2004. He is currently the Defence spokesman, and is a member of the Select Committee on Regulators. He served on the Delegated Powers and Regulatory Reform Select Committee from 2004 to 2006. He became President of the Trading Standards Institute in April 2005.

He has written widely on security topics, and his publications include two books: Can Deterrence Last? and The Technology Trap. He has been writing for a number of security related projects including developments in NATO, European Defence, missile defence proposals and global security issues. He served as a member of the panel of experts for the UK government's 1998 Strategic Defence Review, and gave evidence to the Defence Select Committe on the new threats after 11 September 2001. He was a member of the team developing defence policy for the Liberal Democrat Party, and was an adviser to the Lib Dem defence and foreign affairs teams. He is an elected member of the Liberal Democrat Federal Executive and was on the Federal Policy Committee from 2003 to 2005. He is the President of Liberal International British Group, and also of the Camden Liberal Democrats.

He is a Fellow and Council Member of the Royal United Services Institute (FRUSI)He is an Honorary Fellow of St Catherine's College Oxford, a Fellow and former Council Member of the Royal Aeronautical Society (FRAeS), a Fellow of City & Guilds of London Institute (FCGI) and an Associate Fellow of the Royal Institute of International Affairs . He is a member of the International Institute for Strategic Studies,the Fabian Society. the British Association for the Advancement of Science, the Foreign Policy Centre, the Centre for European Reform, the Pugwash Conference, the UK Defence Forum, the Liberal Democrat European Group the Centre:Forum and of the Anglo-Jordanian Society. He is also a member of advisory boards to the Königswinter Conference, the Oxford Research Group, and the Cambridge University Centre of International Studies. He was a member of the DERA Analysis Board between 1997 and 2000, and was the UK representative to the NATO Defense College in Rome from 1997 to 2001. He is Chairman of the Rippon Group, which acts a focus for EU issues, and is a Patron of Saferworld and Crisis Action. He was made an Honorary Fellow of the US Foreign Policy Association in 1997. He was a Commissioner to the Commission on Globalisation from 2002 to 2004. He is a member of the National Liberal Club, Beefsteak Club, the 63/68 Club, and of the Royal Air Force Club.

He retains his connections with the Services as President of London & South East Region Air Training Corps and as Hon Vice President of the RAF Rowing Club. He was President of the Combined Cadet Force Association from 2000 to 2003. He is a Liveryman of the Guild of Air Pilots and Air Navigators, President of the RAF Oxford & Cambridge Society, and is also a member of Combat Stress and the RAF Historical Society. He is President of the Adastral Burns Club. He is a keen photographer.

He was appointed a CB in 1992 and received his knighthood in 1994. He was appointed as a Chevalier de l'Ordre National de la Légion d'Honneur by President Chirac in July 2003 for his work on European defence issues.

His wife, Sue, is a consultant in vocational training. She was the Parliamentary Candidate for the Liberal Democrats for Finchley & Golders Green for the May 2005 General Election. She was with the City & Guilds of London Institute from 1988 to 2000, and continues to look after Fellowships as an external consultant. She was Chairman of St Hilda's College Association of Senior Members from 1996 to 2000, and President of Middlesex Relate from 1998 to 2002. She is deputy chairman and a Trustee of the Oxford University Society, President of the London Branch, and a Liveryman and the Junior Warden of the World Traders Company. She has been a volunteer worker for SSAFA Forces Help. She became a Vice President of the Institute of Export in 2005.

They have two married graduate daughters: the elder, Alex trained as an engineer, but is now with the NHS, with a son, Jack, and a daughter, Charlotte; and the younger, Antonia, was a primary school teacher, but now runs an educational venture, with two sons, Henry and Thomas.