Background/Objectives: Medication review is an important component of the management of older hospital patients. Deprescribing (supervised withdrawal of inappropriate medicines) is one outcome of review. This study aimed to iteratively develop and test the usability of deprescribing guides, which support multidisciplinary clinicians to reduce inappropriate polypharmacy in older inpatients. Methods: Deprescribing guides for hospital clinicians were developed using a novel mixed-methods, ten-step process. Iterative development and usability testing were applied. This included content development through review of the literature; expert consensus through five rounds of feedback using a modified Delphi approach; and usability testing by 16 multidisciplinary hospital clinicians on hypothetical clinical scenarios involving observations, semi-structured interviews, and administration of the System Usability Scale. Results: This novel process was used to develop deprescribing guides that facilitate implementation of evidence on deprescribing in routine hospital care. The guides present evidence-based information in a format that aligns with workflows of multidisciplinary hospital clinicians. The guides were adapted for various clinical roles to navigate efficiently to suit differing workflow needs. Guides include unique communication support in the form of “preferred language”. Clinicians can use the “preferred language” to apply the evidence to the individual patient and relay decisions between health providers and with patients/carers. The total System Usability Scale score was 80.6 ± 2.0 (mean ± standard error of the mean), indicating excellent usability. Guides have been developed using consistent format for nine medication classes that are common targets for deprescribing and are publicly available. Conclusion: This study demonstrates a novel approach to the development and implementation of evidence-based recommendations that support deprescribing in routine hospital care.