General Sir Mark Alexander Popham Carleton-Smith, GCB, CBE (born 9 February 1964), is a senior British Army officer who served as Chief of the General Staff from June 2018 to June 2022. He previously served as Director Special Forces and commanded 22 Special Air Service Regiment.

Carleton-Smith was commissioned into the Irish Guards on 3 September 1982, before going up to Durham, graduating as BA. He was promoted to lieutenant on 6 September 1985 (with seniority from 9 April), then to captain on 9 April 1989, and then to major on 30 September 1995. After operational service in Northern Ireland during the Troubles, he was deployed to the Gulf War in 1991, and then saw active service as an SAS squadron commander in Bosnia later in the 1990s.

Promoted to lieutenant colonel on 30 June 2001, Carleton-Smith became Military Assistant to the Commander-in-Chief, Land Forces, becoming Commanding Officer of 22 Special Air Service Regiment in 2002. After serving during the 2003 invasion of Iraq and also during operations in Afghanistan, he was an advanced Officer of the Order of the British Empire (OBE) on 23 April 2004. Promoted colonel on 30 June 2005, he became Deputy Director Policy Planning at the Ministry of Defence at that time.

General Staff by General Sir Patrick Sanders in June 2022, Carleton-Smith was promoted Knight Grand Cross of the Order of the Bath (GCB) in the 2023 Birthday Honors. Carleton-Smith served as Regimental Lieutenant Colonel of the Irish Guards from 18 March 2012 for ten years, and as Honorary Colonel of Oxford University Officers Training Corps between February 2017 and June 2022.