Despite improved clinical outcomes of initiating antiretroviral therapy (ART) soon after diagnosis, conflicting evidence exists regarding the impact of same-day ART initiation on subsequent clinical outcomes. We aimed to characterize the associations of time to ART initiation with loss to care and viral suppression in a cohort of newly diagnosed people living with HIV (PLHIV) entering care after Rwanda implemented a national “Treat All” policy. We conducted a secondary analysis of routinely collected data of adult PLHIV enrolling in HIV care at 10 health facilities in Kigali, Rwanda. Time from enrollment to ART initiation was categorized as same day, 1–7 days, or >7 days. We examined associations between time to ART and loss to care (>120 days since last health facility visit) using Cox proportional hazards models, and between time to ART and viral suppression using logistic regression. Of 2,524 patients included in this analysis, 1,452 (57.5%) were women and the median age was 32 (interquartile range: 26–39). Loss to care was more frequent among patients who initiated ART on the same day (15.9%), compared with those initiating ART 1–7 days (12.3%) or >7 days (10.1%),p< .001. In multivariable analyses, same-day ART initiation was associated with a greater hazard of loss to care compared with initiating >7 days after enrollment (adjusted hazard ratio 1.39, 95% confidence interval: 1.04–1.85). A total of 1,698 (67.3%) had available data on viral load measured within 455 days after enrollment. Of these, 1,476 (87%) were virally suppressed. A higher proportion of patients initiating ART on the same day were virally suppressed (89%) compared with those initiating 1–7 days (84%) or >7 days (88%) after enrollment. This association was not statistically significant. Our findings suggest that ensuring adequate, early support for PLHIV initiating ART rapidly may be important to improve retention in care for newly diagnosed PLHIV in the era of Treat All.