This study aims to use Art brut works—the artwork of the socially underprivileged and alienated—to influence social roles in fashion design, employing a formative expression method to promote social acceptance of diversity in the industry. The research method involved investigating Art brut’s concept and evolution in domestic and foreign literature and previous studies. The formative characteristics of the movement were derived by analyzing the works of Art brut artist Johann Hauser. One hundred and twenty images of Johann’s work were collected through online sources like the Gugging Museum’s website, Christian Berst Gallery’s website were developed as fashion design using the CLO 3D program. The formative characteristics of Johann’s works appeared to be transparent overlapping, divisional decorativeness emphasized simplicity, and vibrant chromaticity. Based on this analysis, the results of the 3D digital fashion designs were as follows. First, the characteristics of the atypical objects and figures in Johann’s works were applied to the design silhouette, revealing a uniquely beautiful form. Second, Johann used a method in which numerous line shapes overlap and fill the area. The point of connecting the work is expressed as a graphic pattern by decorating the lines of the hem and hem of the garment with piping or attaching overlapping straps on top of pants and dresses. Third, the combination of overlapping colors used in Johann’s work is a color block design of fashion, which utilizes the formative fun.