The World Health Organization (WHO) recommends universal antiretroviral therapy (ART) for people living with HIV (PLWH), but evidence about effects of expanded ART access on ART retention in low-resource settings is limited.Haiti's Ministry of Health endorsed universal ART for pregnant women in March 2013 (Option B+) and for all PLWH in July 2016. This study included 51,579 ART patients from 2011-17 at 94 hospitals and clinics in Haiti.This observational, retrospective cohort study described time trends in 6-month ART retention using secondary data, and compared results during three time periods using an interrupted time series (ITS) model: pre-Option B+ (period 1: 1/11-2/13), Option B+ (period 2: 3/13-6/16), and Test and Start (T&S, period 3: 7/16-9/17).From the pre-Option B+ to the T&S period, the monthly count of new ART patients increased from 366/month to 877/month, and the proportion with same-day ART increased from 6.3% to 42.1% (p<0.001). The proportion retained on ART after 6 months declined from 78.4% to 75.0% (p<0.001). In the ITS model, ART retention improved by a rate of 1.4% per quarter during the T&S period after adjusting for patient characteristics (Adjusted Incidence Rate Ratio [aIRR]=1.014; 95% confidence interval [CI]: 1.002-1.026, p<0.001). However, patients with same-day ART were 14% less likely to be retained compared to those starting ART >30 days after HIV diagnosis (aIRR=0.86; 95% CI: 0.84-0.89, p<0.001).Achieving targets for HIV epidemic control will require increasing ART retention and reducing the disparity in retention for those with same-day ART.