[8] He became Military Assistant to the Chief of the General Staff in 1973 and, following a year as Second in Command of 1st Battalion Welsh Guards in London and Cyprus[8] and having been promoted to lieutenant colonel on 31 December 1975,[10] he became brigade major for the Household Division in 1976.

[1] Guthrie was appointed a Member of the Royal Victorian Order (MVO fourth class) in the 1977 Silver Jubilee and Birthday Honours; on 31 December 1984 this rank was reclassified as Lieutenant (LVO).

[1] Promoted to colonel on 31 December 1979,[12] he undertook a tour of duty in Northern Ireland in Spring 1980 for which he was appointed an Officer of the Order of the British Empire.

[24] Guthrie then became Chief of the General Staff (CGS) on 15 March 1994,[25] being advanced to a Knight Grand Cross of the Order of the Bath in the Queen's Birthday Honours 1994.

[36][37] He was one of several retired Chiefs of Defence Staff who spoke out in the House of Lords about the risk to servicemen facing liability for their actions before the International Criminal Court, particularly with respect to the invasion of Iraq.

Monbiot based his argument on Guthrie's September 2002 statement for an invasion of Iraq and subsequent comments, in which he appeared to support launching "surprise wars", something forbidden by the United Nations Charter.

[40] In 2007 Guthrie co-authored a book on ethics in modern warfare with Sir Michael Quinlan, formerly Permanent Secretary of the Ministry of Defence.

[48] He is president of several charities, including Action Medical Research, the Army Benevolent Fund, Soldier On!,[49] and the Progressive Supranuclear Palsy Association.

[55] In August 2014, Lord Guthrie was one of 200 public figures who were signatories to a letter to The Guardian opposing Scottish independence in the run-up to September's referendum on that issue.

[57] He is on the advisory board of Veterans for Britain an organization with the stated aim of supporting " Her Majesty's Government in the task of restoring full sovereign control to all aspects of the defence of the Realm " following the EU referendum.

[58] Since 1 August 2017 Lord Guthrie has been the Senior Advisor to Ron Wahid, Chairman of Arcanum, a subsidiary of Magellan Investment Holdings.

[63] On 8 January 2019, in an extraordinary intervention in the political sphere by figures from the military and intelligence services quarter, Guthrie sent a letter, co-signed by Sir Richard Dearlove, to Conservative Party Parliamentary Constituency Association Chairs, stating that the passage through the House of Commons of Prime Minister Theresa May's Withdrawal Agreement of the United Kingdom from the European Union contained decisions which fundamentally undermined the integrity of the Defence of the Realm, and requested they take measures to discourage their parliamentary representatives from voting for it imminently in the Commons.

The letter as an alternative advocated the case upon national security grounds that the United Kingdom should fully withdraw from the European Union without an Intergovernmental relationship between the two persisting after the process.