His most important realisations include the Paderewski housing estate (1967-1969) designed in collaboration with Jurand Jarecki and Ryszard Ćwikliński, and a collection of edifices in Korfanty Avenue in Katowice, completed in the 1960s, consisting of the office block named Separator, an exhibition pavilion of the Biuro Wystaw Artystycznych (Artistic Exhibitions Bureau) and the 20-storey residential block Ślizgowiec. These buildings played their part in a major reorganization of the city centre in the spirit of late modernism planned after the war.
One of the most interesting projects by Kwaśniewicz is the abode of Śląski Instytut Naukowy (the Silesian Scientific Institute, completed in 1977), which is now in ruins. Because of its difficult location next to a busy intersection, and a small parcel of land surrounding it, its workshops and conference rooms were only open to its inner patios. The skeleton construction was based on a module of squares, connected by hinged joints. This low, compact building seems lighter thanks to its splayed edges and to the columns on which it is placed. Triangular incisions in the facade form the main decoration of the building, making it more dynamic.
Between 1959 and 1965 the architect designed (together with Jurand Jarecki) the Kosmos cinema on Grunwaldzki Square – the first panoramic cinema in Katowice. Its characteristic element was a spacious, two-level hall, with glass walls facing the park. A polychrome by Zbylut Grzywacz was placed on one of the walls. Although the materials used for the project were of low quality (aluminium columns that mimic chrome), Kosmos was one of the best realisations of late modernism in Katowice, but modern renovation has totally changed the character of the building.
Other important projects outside of Katowice were a shopping mall in Jastrzębie Zdrój, the Dobry Pasterz and Matka Boska Częstochowska churches in Drogomyśl (1966-1969), and a parish church in Wrzosowa, next to Częstochowa, which was completed in 1978. Both churches were expressive in form, which was typical of sacral architecture in the 1970s. The new building of the Biblioteka Śląska (Silesian Library) in Katowice, one of Kwaśniewicz's later projects created in collaboration with Jurand Jarecki and Marek Gierlotka as a result of a contest organised in 1989 (built between 1991 and 1997), is also worth mentioning. The enormous, clear building fits well with the urban environment and the surrounding greenery. The solid of the magazine grows out of an octagonal base surrounded by an embankment, hiding garages and reading and utility rooms. The architects decided to reference Silesian modernism – the columns on which the magazine is placed were inspired by the simple modernist colonnades that are often found in Katowice, and the monumental form of the building is reminiscent of the late modern architecture of the city. Thanks to its diagonal axis, the facade was placed on the shorter side of the construction. The entrance was marked by an openwork gate covered with black stone which was supposed to evoke coal. The building's biggest benefit is its functional arrangement and technological use, which distinguishes it among Polish libraries.