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. 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.