The building was to have a temporary character and could later be used for other purposes - this was the explicit brief that architect Egon Eiermann had to fulfill in 1965 when planning the New Parliamentary Tower in Bonn. In the event of a move to Berlin, the building was to be offered to international organizations as their headquarters, the Presidium of the Bundestag suggested at the time.

However, what was considered extremely unlikely during the Cold War became reality: in 2006, seven years after the members of the Bundestag left the "Lange Eugen", the landmark of parliamentarianism in Bonn, in 1999, UN Secretary-General Kofi Annan inaugurated the listed building as the centerpiece of the UN Campus.

The furnishing of the offices in the "Lange Eugen" is strictly based on the original furnishings, right down to the veneer of the built-in cupboards and shelves. Even though walls were removed in many rooms to create space for several workstations, the style was retained: 40,000 square meters of French walnut wood were used to recreate cabinets and doors, 10 kilometers of shelves and 14 kilometers of skirting boards were replaced.

Following the refurbishment of the "Lange Eugen", 410 offices, four conference rooms, 36 meeting rooms and a large library are now available. The cost of the refurbishment, which lasted from 2002 to March 2006, amounted to 55 million euros.

New features include mobile flood protection walls, which can be attached to the foundations around the building within three hours, and meter-thick flood protection panels under the building to prevent water ingress from below. Interpreter booths for up to seven languages in the large meeting rooms, two video conference rooms and glass fire protection walls were also added. There is also an internet café for UN staff as well as a prayer and meditation room.

The UN organizations use the buildings of the UN Campus rent-free, but pay for the operating costs. Thanks to energy-efficient building refurbishment, however, these are significantly lower than in the days of the German capital.

The German government has always advocated the expansion of the UN site and has taken steps to create its own UN campus to support the work of the UN organizations based in Bonn. On July 11, 2006, the flag of the United Nations was raised in front of the "Langen Eugen". German Chancellor Angela Merkel officially handed over the now extraterritorial area to UN Secretary-General Kofi Annan and opened the historic building together with him.

Today, the growing UN Campus provides space for numerous UN organizations with a total of around 1,000 employees. In addition to the former parliament buildings of the Federal Republic of Germany, another building is currently under construction on the campus site, which is due to be occupied in 2020.

A state-of-the-art international conference center - the  World Conference Center Bonn (WorldCCBonn) - is located in the immediate vicinity of the UN Campus. The former plenary hall building of the German Bundestag now forms part of this conference center. An impressive extension has been built next to it.

The original UN headquarters in Bonn, Haus Carstanjen, is located nearby and is still used by the United Nations.

The constant expansion of the Bonn "United Nations Campus" is evidence of the growing presence of the United Nations in Bonn. As the German city of the United Nations, Bonn's UN Campus offers the right infrastructure to permanently anchor the United Nations in Bonn.