Promoted to brigadier general in 2013, Claesson held key leadership roles, such as commanding the Swedish ISAF contingent in Afghanistan and overseeing Nordic Battlegroup training.

He also did two years as a teacher at the company management course (KHS HK) at the Swedish Armoured Troops Combat School (Pansartruppernas stridsskola, PS) in Skövde.

He also attended the higher course from 1990 to 1991 when he was promoted to captain, and the Tactical Course for the Army (Taktisk kurs för Armén, TAK A) at the Swedish National Defence College in Stockholm from 1994 to 1995.

He was then a student at the German Armed Forces Language Agency (Bundessprachenamt, BSprA) in Hürth, Germany from 1 February 1997 to 31 August 1997.

Claesson then served as a military expert at the Ministry of Defence's Unit for Security Policy and International Affairs (Enheten för säkerhetspolitik och internationella frågor, Fö SI) from 1 November 2002 to 30 April 2003 and as commander and head of and training of Norrbotten Armoured Battalion in Norrbotten Regiment (I 19) in Boden from 1 May 2003 to 28 February 2005.

Promoted to brigadier general in 2013, he served as a military adviser to the Ministry for Foreign Affairs in Stockholm from 24 June 2013 to 28 February 2015.

Claesson was then Deputy Chief of Policy and Plans Department in the Defence Staff at the Swedish Armed Forces Headquarters from 1 March 2015 to 30 September 2018.

[6] On 7 June 2024, Claesson was appointed general and Chief of Defence, and took office on 1 October 2024 after a formal handover ceremony at Karlberg Palace.