Following the principles of sustainable marketing, any organization should meet the needs of its current consumers without compromising the ability of future generations to fulfill their own needs. This concern is valid not only for the environment but also the sustainability’s economic and social dimensions. The clothing industry is adapting business models to meet environmental awareness and demand for sustainable clothing. This study aims to understand how the clothing business and consumer behavior are changing in consideration of sustainability. Specifically, it addresses how fashion consumers consider sustainability when selecting and purchasing clothing, contrasting slow and fast fashion approaches. Firstly, an exploratory quantitative study based on an online survey about slow fashion purchase intention was performed with a sample of 864 Portuguese residents. Analyses of descriptive statistics (means, frequencies, and Cronbach’s alpha) and inferential statistics (chi-square, t-test, and ANOVA) were used. Then, a single-case study of a well-known Portuguese fashion brand concerning its strategy towards sustainability was carried out. The study concludes that there are positive associations between the consumer consideration for sustainability and slow-fashion clothing and the consumer perceived value, purchase intention, willingness to pay a price premium, and recommend slow-fashion products.