Since 24 June 2005, the Crown Prince has been a member of the Council of State. He regularly attends the plenary sessions and various committees. This enables him to deepen his knowledge of the institutional and legislative workings of the country.

Since his appointment as Hereditary Grand Duke, Prince Guillaume has accompanied his parents to numerous representative and institutional activities, such as National Day celebrations, New Year's Audiences granted to national authorities, as well as many State and official visits.

The Prince is personally involved in the duty of remembrance. Because Grand Duke Jean, his grandfather, fought in World War II, these commemorations hold a deep meaning for him. Since he was sworn in as Crown Prince, Prince Guillaume has attended national and international commemorations of World War II, such as the commemoration of the 70th anniversary of the Liberation of Vianden and the Auschwitz-Birkenau and the Mauthausen concentration camps in 2015. He accompanied an educational, cultural and commemorative journey with young people joining the Témoins de la Deuxième Génération ASBL (Second Generation Witnesses ASBL) and the Krakow/Auschwitz ASBL in 2016. In 2019, he attended the commemoration of the 75th anniversary of the Battle of the Bulge at Schumannseck.