Carter was promoted to colonel on 31 December 2000 (with seniority from 30 June) and advanced to Commander of the Order of the British Empire on 29 April 2003, following service in the War in Afghanistan.
He was promoted brigadier on 31 December 2003 (with seniority from 30 June), and in 2004 he was given command of 20th Armoured Brigade, commanding British forces in Basra, at one point stating that British forces could be in Iraq for "as long as a decade".
On 7 September 2004 he was awarded a further Queen's Commendation for Valuable Service for his service in Iraq.

Carter became Director of Army Resources and Plans at the Ministry of Defence in 2006 and was given the honorary appointment of Deputy Colonel of The Rifles on 1 February 2007 (the successor regiment to the Royal Green Jackets) – a post he held until 1 November 2009.
Promoted to major general on 23 January 2009, became General Officer Commanding 6th Division which was deployed to Afghanistan with Carter as Commander ISAF Regional Command South.
In September 2009, referring to the efforts of UK and NATO forces, Carter said that "time was not on our side".
After returning to the UK in November 2010, he gave an interview in which he warned that "the insurgency is resilient, and alive and well".

Carter became Director-General Land Warfare early in 2011 and, 
having been awarded the Distinguished Service Order in March 2011, he was promoted to lieutenant general and appointed Commander Field Army in November 2011 (the role redesignated Deputy Commander Land Forces in January 2012).
He was the main architect of the Army 2020 concept and reported on his recommendations in April 2012.
He assumed the post of Deputy Commander, International Security Assistance Force (ISAF), under the command of American general, John R. Allen, in September 2012 and, having handed over his command at ISAF in July 2013, he became Commander Land Forces in November 2013.

Carter was appointed Knight Commander of the Order of the Bath (KCB) in the 2014 New Year Honours.
On 21 February 2014 it was announced that Carter would assume the post of Chief of the General Staff.
He took up his post and was promoted to full general on 5 September 2014.
As of 2015, Carter was paid a salary of between £170,000 and £174,999 by the department, making him one of the 328 most highly paid people in the British public sector at that time.
Carter was awarded the US Legion of Merit on 18 March 2016 for services in Afghanistan.

On 1 February 2013, he succeeded Sir Nick Parker as Colonel-Commandant of The Rifles.

In January 2018 Carter used a speech in London to enter publicly into the debate over defence spending.
According to Carter failure to keep up with Russia will leave the UK exposed, particularly to unorthodox, hybrid warfare.
He also said that one of the biggest threats posed is from cyber-attacks that target both military and civilian life.
Carter said: "Our ability to pre-empt or respond to threats will be eroded if we don't keep up with our adversaries."

In June 2018 Carter succeeded Air Chief Marshal Sir Stuart Peach as Chief of the Defence Staff.

In August 2018 Carter said he would not allow British soldiers to be "chased" by people making "vexatious claims" about their conduct during the Troubles in Northern Ireland.
Carter said serving and former service personnel should face action for "genuine" wrongdoing.
But he vowed groundless cases "will not happen on my watch".

In 2018 Carter also became the patron for the UK charity Supporting Wounded Veterans.

Carter was appointed Knight Grand Cross of the Order of the Bath (GCB) in the 2019 Birthday Honours.

In 2020, Carter was one of the senior public servants who took part in the Government's daily coronavirus briefings.
Carter was promoted to colonel on 31 December 2000 (with seniority from 30 June) and advanced to Commander of the Order of the British Empire on 29 April 2003, following service in the War in Afghanistan. He was promoted brigadier on 31 December 2003 (with seniority from 30 June), and in 2004 he was given command of 20th Armoured Brigade, commanding British forces in Basra, at one point stating that British forces could be in Iraq for "as long as a decade". On 7 September 2004 he was awarded a further Queen's Commendation for Valuable Service for his service in Iraq.
Carter became Director of Army Resources and Plans at the Ministry of Defence in 2006 and was given the honorary appointment of Deputy Colonel of The Rifles on 1 February 2007 (the successor regiment to the Royal Green Jackets) – a post he held until 1 November 2009. Promoted to major general on 23 January 2009, became General Officer Commanding 6th Division which was deployed to Afghanistan with Carter as Commander ISAF Regional Command South. In September 2009, referring to the efforts of UK and NATO forces, Carter said that "time was not on our side". After returning to the UK in November 2010, he gave an interview in which he warned that "the insurgency is resilient, and alive and well".
Carter became Director-General Land Warfare early in 2011 and, 
having been awarded the Distinguished Service Order in March 2011, he was promoted to lieutenant general and appointed Commander Field Army in November 2011 (the role redesignated Deputy Commander Land Forces in January 2012). He was the main architect of the Army 2020 concept and reported on his recommendations in April 2012. He assumed the post of Deputy Commander, International Security Assistance Force (ISAF), under the command of American general, John R. Allen, in September 2012 and, having handed over his command at ISAF in July 2013, he became Commander Land Forces in November 2013.
Carter was appointed Knight Commander of the Order of the Bath (KCB) in the 2014 New Year Honours. On 21 February 2014 it was announced that Carter would assume the post of Chief of the General Staff. He took up his post and was promoted to full general on 5 September 2014. As of 2015, Carter was paid a salary of between £170,000 and £174,999 by the department, making him one of the 328 most highly paid people in the British public sector at that time. Carter was awarded the US Legion of Merit on 18 March 2016 for services in Afghanistan.
On 1 February 2013, he succeeded Sir Nick Parker as Colonel-Commandant of The Rifles.
In January 2018 Carter used a speech in London to enter publicly into the debate over defence spending. According to Carter failure to keep up with Russia will leave the UK exposed, particularly to unorthodox, hybrid warfare. He also said that one of the biggest threats posed is from cyber-attacks that target both military and civilian life. Carter said: "Our ability to pre-empt or respond to threats will be eroded if we don't keep up with our adversaries."
In June 2018 Carter succeeded Air Chief Marshal Sir Stuart Peach as Chief of the Defence Staff.
In August 2018 Carter said he would not allow British soldiers to be "chased" by people making "vexatious claims" about their conduct during the Troubles in Northern Ireland. Carter said serving and former service personnel should face action for "genuine" wrongdoing. But he vowed groundless cases "will not happen on my watch".
In 2018 Carter also became the patron for the UK charity Supporting Wounded Veterans. 
Carter was appointed Knight Grand Cross of the Order of the Bath (GCB) in the 2019 Birthday Honours.
In 2020, Carter was one of the senior public servants who took part in the Government's daily coronavirus briefings.
Nick Carter (British Army officer)