Together with Josy Goerres, Krieps founded the Resistance organisation "Service d'Action et de Renseignement des Patriotes Indépendants" (SAR-PI-MEN).
[1] However, on 20 May 1942, he was released for medical reasons, and he immediately started working with the PI-MEN in Differdange again, which was a stronghold of the Resistance.
[1] Finally, he manage to arrive in Britain (via Portugal) on 29 June 1943, where he joined the Belgian army, and received training as a parachutist and at the British Military Intelligence School.
In London he also had the opportunity to participate in one of the Luxembourgish government-in-exile's cabinet sessions, in order to deliver a detailed report on occupied Luxembourg.
[1] In 1946, the Resistance member Norbert Gomand was taken to court by the government for libel, as in his newspaper L'Indépendant he had accused the government-in-exile of treason and gross negligence for failing to do more to help Luxembourgers under occupation.
[1] Later in the same year, in connection with the Gomand trial, Krieps was implicated in the event known as the "Putsch of the officers", an alleged coup d'état.
When obligatory military service was abolished, he left the army on 31 December 1967 to go into politics, joining the Democratic Party on 1 January 1968.
[1] On 9 July 1971 he joined the second Werner-Schaus government as secretary of state in the Ministry for the Interior, with responsibility for nature conservation and construction planning in the communes and cities.
[1] As Minister for Health, he left a long-lasting legacy, including the law creating the "Centre Hospitalier" and a health system that stuck a balance between state and private healthcare; the enlargement of the thermal spa in Mondorf; the modernisation of the "Maison de Santé" in Vianden, the law on the new pavilion in Ettelbrück and the hospital "Princesse Marie-Astrid" (HPMA) in Differdange.
[1] After the elections of 1984, the Democratic Party left the government, and he sat as an opposition Deputy for the Centre constituency until 1994, when he retired from active politics.
His son Alexandre Krieps was also active in the Democratic Party and was likewise a member of the Chamber of Deputies for several years.