However, he changed his study program and graduated in educational sciences at the Haute Ecole Robert Schuman in Virton, Belgium.

In his candidate speech, Delles emphasized the importance to combat climate change and the, in his eyes, ambitious targets the Luxembourg government had set.

He called zero growth and austerity policies the wrong approach to the climate crisis and claimed that the willingness of the economy to switch to climate-friendly alternatives was "immense".

[13] After the 2013 general election, then-mayor Maggy Nagel became Minister of Culture and Public Housing, an office incompatible with being mayor.

[14] However, he decided to form another coalition with The Greens, citing his friendship with and loyalty to Alderman Steve Schleck as reason.

[7] As part of his municipal responsibilities, Delles was chairman of the Syndicat intercommunal pour la création, l'aménagement, la promotion et l'exploitation d'une zone d'activités économiques à caractère régional dans le canton de Remich (SIAER - Triangle vert) from March 2014 until December 2018.

He was a member of the commissions on civil service and administrative reform; on agriculture, viticulture, rural development and consumer protection; on culture; on petitions; on public housing; on Higher Education, Research, Media, Communications and Space (for the Higher Education and Research aspects); and on Institutions and Constitutional Review (for certain law projects).

[1][17] During his mandate, Delles asked a total of 45 parliamentary questions, often related to local matters in his constituency or his home town of Mondorf-les-Bains, where he mayor.

[47][48] At the beginning of his term, Delles stated his priorities were the strengthening of congress tourism, regulation of homestay providers such as Airbnb, the expansion of tourist cycling and hiking trails and, for small and medium-sized enterprises, a reform of the law on shop opening hours.

One measure was the issuing of 50 Euro hotel vouchers to all Luxembourg residents over the age of 16 and all cross-border commuters in order to boost tourism in the Grand Duchy.

[53] Other measures to promote domestic tourism introduced in 2020 were a service to transport luggage from one hotel to another when tourists were cycling or hiking and the Vëlosummer (bike summer).

However, nine communes vetoed the plans on their territory and other routes were changed in a manner that the project was a lot smaller than presented at the beginning.

[56] In May 2021, Delles announced the Grand-Duchy of Luxembourg would buy back the boat MS Regensburg previously known as Marie-Astrid II, which was floating on the river Moselle when the Schengen agreement was signed on 14 June 1985.

[62] At the end of his term, Delles stated that he had reduced the processing time for business establishment licences to less than seven days on average.

He also introduced new assistance for start-ups and passed a law that gives entrepreneurs a second chance so that they are no longer excluded from setting up another company in the event of bankruptcy.

[7] Delles also emphasised the importance of ecologically sound tourism, which would attract nature loving tourists to Luxembourg.

[62] During the campaign for the 2023 general election, Delles was again lead candidate for the DP in the East constituency, together with Carole Hartmann.

Delles was part of the DP delegation coalition talks between the CSV and his party, which resulted in the formation of the Frieden-Bettel government.

As competences shifted with the new coalition treaty, external trade was now one of the responsibilities of the new Foreign Minister Xavier Bettel.

[65] In December 2023, Delles stated that his priorities for the new legislative period were the development of new areas for business parks and the expansion of Luxembourg's data centre capacities for artificial intelligence.