HIV disproportionately affects sexual minority men (SMM; eg, gay, bisexual, and other men who have sex with men) in Lima, Peru; epidemiological data estimate that 32% to 39% of new HIV infections occur among adult cisgender SMM within primary partnerships (ie, male couples). Most HIV prevention-care research in Lima, Peru, has focused on SMM as individuals and not couples. To help address this critical gap in prevention care, we developed Para Ti, Para Mí, Para Nosotros (P3): a couples-based, digital HIV serostatus-neutral intervention (DHI) for adult cisgender SMM couples in Lima, Peru. The P3 DHI is designed to facilitate couples with skill-building, communication, decision-making, and working together to form and adhere to a detailed prevention care plan that aligns with their explicit sexual agreement. The P3 DHI is theoretically informed, self-guided, directed, sequential, and fully automated. This pilot randomized controlled trial (RCT) aims to examine the preliminary effects of P3 on couples' formation and adherence to a detailed prevention care plan containing evidence-based strategies that also aligns with their explicit sexual agreement over time. In addition, the feasibility of enrollment and retention and couples' acceptability of P3 will be assessed. The research implements a prospective, 6-month pilot RCT with a 3-month delayed control condition. After baseline, 60 enrolled SMM couples will be randomized to 1 of 2 conditions. Couples randomized to the unmatched, delayed control condition will receive access to the P3 DHI to use during the last 3 months of the trial after the 3-month assessment. Couples randomized to the immediate intervention condition will immediately receive access to the P3 DHI for 6 months. Study assessments will occur at baseline and months 3 and 6. Descriptive, comparative, qualitative, and longitudinal analyses using generalized linear mixed-effect, multilevel, and actor-partner interdependence models will be conducted to address the specific aims. The 6-month pilot RCT is ongoing. Recruitment, enrollment, and data collection began in January 2023 and ended in April 2024. A total of 74 adult cisgender SMM couples met all inclusion criteria, provided consent, and were enrolled in the pilot RCT. Retention was 92% (68/74) at month 6. Data are currently being analyzed to address the 3 specific aims regarding feasibility, acceptability, and preliminary efficacy. Findings from this research will reveal whether couples deemed the P3 DHI to be acceptable. Findings will also highlight the preliminary efficacy of the P3 DHI on couples managing their vulnerability to HIV and other sexually transmitted infections (STIs) over time via alignment of their prevention-care plan and sexual agreement. Trial findings will help shape the future direction of the P3 DHI while addressing the existing gap in prevention and care services for couples in the local context. ClinicalTrials.gov NCT05873855; https://clinicaltrials.gov/study/NCT05873855. DERR1-10.2196/63106.