While holding this position, he made overseas trips to Uruguay, Mozambique, Argentina, Peru, Bolivia, Spain, Tunisia and Australia (twice) to assess the potential of mining concessions, earning a high reputation among financiers.

After the war he went to Paris in March 1871 and studied briefly at the Collège Sainte-Barbe before being admitted to the École Polytechnique in the promotion of 1871.

[3] Henry Küss was appointed a 3rd class engineer in 1877, and for a year was attached to the Secretariat of the General Council of Mines, and also was entrusted with a district of the Chemins de fer de l'Est (Eastern Railways) under the supervision of one of his uncles, Adolphe Küss, chief engineer of Ponts et Chaussées.

From May to December 1881 he was attached to a Portuguese mineral exploration mission in the Zambezi region, where he investigated possible gold deposits around the settlement of Tete.

[2] He observed in a letter to his family, The first thing I saw, was a pair of posters with black borders, announcing the death of two Division Engineers, Petit and Sordoillet.

In the central section – Culebra Hill – where the Company is committed to extract 750,000 cubic meters a month, it hardly reaches 30 to 40,000.

[2] In 1888 Küss married Cécile Jeanne Weiss, daughter of a Registry official from Alsace whom he had met in Grenoble.

Küss visited Tunisia in 1892 at the request of the Compagnie des chemins de fer Bône-Guelma to evaluate lead and zinc deposits in the Medjerda valley.

[2] In the fall of 1890 the post of ordinary engineer of the western mineralogical sub-district of the Saint-Étienne coal basin became vacant.

The Minister of Public Works wanted an engineer who could reassure the mine workers and force the operators to improve safety measures.

[2] To reassure critics who denounced training of civil servants and thought over-rapid improvement in the social status of workers would be dangerous, in 1905 Henry Küss stated that the pupils did "not need a very extensive scientific background, which they would anyway with very few exceptions be unable to assimilate.

He was fluent in English, German and Spanish, and was well-qualified to represent the Ministry of Public Works in international conferences.

In August 1910 he visited the Brussels Exhibition and the Belgian Coal Basins to study facilities for hygiene of mining workers.

[2] The editors of the Encyclopédie théorique et pratique des connaissances civiles et militaires wanted to add a treatise on exploitation of mines.

Henry Küss collaborated with Lucien François Fèvre (1862–1935) on this work, whose first instalment was published in July 1897.

On 20 February 1914 Küss was appointed head of the École nationale supérieure des mines de Paris in succession to Frédéric Delafond, scheduled to start in August.