Pre-exposure prophylaxis (PrEP) has emerged as a prominent approach for the prevention of HIV infections. While the latest advances have resulted in effective oral and injectable product options, there are still gaps in on-demand, event-driven, topical products for HIV prevention that are safe and effective. Here we describe the formulation development of a dual-compartment topical insert containing tenofovir alafenamide fumarate (TAF) and elvitegravir (EVG) that may be administered when needed, vaginally or rectally, pre- or post-coitus, for flexible HIV prophylaxis. Specifically, we describe the lab-scale formulation development, preclinical mucosal safety and pharmacokinetics (PK) testing in rabbits, long-term stability, and scale-up clinical manufacturing of the lead TAF/EVG (20 mg/16 mg) inserts, which are currently in clinical stages of development. As designed, the inserts are small, discreet and portable, offering a number of promising attributes, such as simple and robust direct-compression manufacturing, fast initial disintegration/dissolution, and suitable mechanical strengths showing low hardness (<8 kg), friability (<1 %), and moisture content (<1 %). The inserts initiated disintegration quickly (∼ ≤ 15 min) providing full in vitro release (>90 %) of TAF and EVG within 60 min of dissolution. The lead insert was selected from formulation prototypes that met the evaluation criteria for manufacturability and characterization, along with a dose-ranging PK study in non-human primates. Successful technology transfer for clinical development of the lead TAF/EVG (20 mg/16 mg) insert was confirmed under current Good Manufacturing Practices (cGMP) conditions. Based on the 12 months (lab-scale) and 24 months (clinical batch) stability data, the TAF/EVG inserts are projected to have a long shelf life of over 2 years, if stored at or below 30 °C/65 % RH. Overall, these newly designed topical inserts have formulation properties that enable stable storage and fast release of the antiretroviral payload from a small, portable and discreet dosage form. They are safe and effective when applied vaginally or rectally, before or after coitus, providing the basis for a new method of flexible on-demand HIV prevention for cisgender and transgender women and men. The TAF/EVG inserts are currently the most clinically advanced on-demand topical product, as attested by their completed and ongoing clinical trials.