Background/Objectives: Given the limitations of traditional approaches to treating existential distress in seriously ill patients, psilocybin-assisted therapy (PAT) has emerged as a promising treatment option. However, weighing up the potential risks and benefits of this approach can be challenging for both healthcare professionals and patients. Decision aids can play a key role in supporting shared decision making by clarifying options, improving knowledge, and enhancing decision quality. To date, there is no decision aid specific to PAT. This descriptive study aimed to develop a decision aid for individuals considering this therapy. Methods: A paper-based/electronic decision aid was developed with a multidisciplinary steering committee following the International Patient Decision Aids Standards Collaboration (IPDAS). Development included conducting a literature review and prototype design, evaluating acceptability and usability by potential users (i.e., patients and healthcare professionals), and producing a final version. Questionnaires, direct feedback, and semi-structured interviews with potential users allowed for evaluation and refinement of design and content. Results: The final version of the decision aid is presented as a booklet, covering areas such as PAT education, comparison of treatment options, and personal reflection. Feedback from patients (n = 5) and healthcare professionals (n = 5) guided improvements, helping clarify content, ensuring balanced information, optimizing its length for usability, and providing decision-making support. Conclusions: The decision aid developed in this study demonstrated satisfactory acceptability and usability, meeting IPDAS criteria. By providing balanced and accessible information, it may facilitate shared decision-making for individuals considering PAT, representing a significant step forward in this emerging area of palliative care.