The 54-year-old served as Deputy Chief of the Defence Staff (Military Strategy and Operations) since April 2016 and is ex-Special Forces.
He was also promoted as he took the role.
Defence Secretary Gavin Williamson said after his appointment in May:
"I’m delighted to offer my congratulations to Lieutenant-General Carleton-Smith on his appointment of Chief of the General Staff.
"Lt Gen Carleton-Smith has played a leading role in many of our recent operations at home and abroad, including our campaign to defeat Daesh in Iraq and Syria, our support to British Overseas Territories affected by Hurricane Irma and the military’s support to areas badly affected by the snow earlier this year.
"I have no doubt that Lt Gen Carleton-Smith will be an outstanding leader of the Army at this crucial period, as we look to strengthen and further modernise the Army to deal with intensifying threats.
Education: Durham University, BA (Hons) History/Politics
1986: Commissioned into 1st Battalion Irish Guards from the Royal Military Academy Sandhurst.
1986-1998: Served in London, Germany, Canada, South Armagh, the Gulf and The Balkans.
1999-2001: Chief of Staff of 19 Mechanized Brigade. Served two tours in Kosovo as Chief of Staff HQ Multi-National Brigade Centre.
2001-2002: Military Assistant to the Commander-in-Chief Land Forces. Promoted to Lieutenant Colonel.
2002-2005: Assumed regimental command, serving in Iraq and Afghanistan.
2005: Deputy Director Policy Planning in the Ministry of Defencce (MoD). Promoted to Colonel.
2006-2008: Assumed command of 16 Air Assault Brigade. Served in Afghanistan as Commander Helmand Task Force and Commander British Forces Afghanistan.
2009-2011: Head of Army Resources and Plans.
2012: Promoted to Major General.
2015-2016: Director Strategy at Army Headquarters in Andover. Became Deputy Chief of Defence Staff (Military Strategy and Operations) in April 2016.
Challenges Ahead For The New CGS
By Laura Makin-Isherwood, Westminster correspondent, Forces News
Gen Mark Carleton-Smith takes up his position as Head of the Army at an interesting time.
The threats facing the UK are more varied and unpredictable now than at any time since the end of the Cold War and pressure on the service is growing.
At home, in little more than a year, the Army has been called in to assist in the wake of the Westminster Bridge terror attack, in the clean-up operation following the chemical attack in Salisbury, even to help people stranded in the heavy snowfall that swept the nation this March.
Overseas, British troops are stationed in the Baltic States, helping to train Afghan Security Forces and have been deployed on an anti-poaching operation in Malawi.
Britain’s commitment to global security remains high, but the ongoing recruitment crisis, dissatisfaction about pay and accommodation, and MoD budget holes cannot be masked.
It may be Gen Mark Carleton-Smith’s first week, but with the conclusions of the Modernising Defence Programme imminent, he’ll have to get settled into his new role quickly.