Transdisciplinary sustainability science (TSS) is a prominent way of scientifically contributing to the solution of sustainability problems. Little is known, however, about the practice of scientists in TSS, especially those early in their career. Our objectives were to identify these practices and to outline the needs and challenges for early career scientists in TSS. To that end, we compiled 10 key characteristics of TSS based on a literature survey. We then analyzed research groups with 81 early career scientists against these characteristics. All of these research groups are funded by an ongoing federally funded German program for socialecological research whose main feature is to promote sustainability-oriented inter- and transdisciplinary research. We found that the practices of the 12 groups generally correspond with the characteristics for TSS, although there is ample variation in how they were addressed. Three major challenges were identified: (1) TSS demands openness to a plurality of research designs, theories, and methods, while also requiring shared, explicit, and recursive use of TSS characteristics; (2) researchers in TSS teams must make decisions about trade-offs between achievements of societal and scientific impact, acknowledging that focusing on the time-consuming former aspect is difficult to integrate into a scientific career path; and (3) although generalist researchers are increasingly becoming involved in such TSS research projects, supporting the integration of social, natural, and engineering sciences, specialized knowledge is also required.