Background Unwanted pregnancies remain a burden for women living with HIV (WLWH). Family planning prevents unplanned pregnancies while promoting longer birth intervals, key strategies to eliminate perinatal transmission of HIV and promote maternal and child health. We evaluated the effect of a family planning voucher, inclusive of immediate postpartum counseling, on uptake, early initiation, and continuation of modern contraceptive methods among recently postpartum WLWH delivering at a publicly funded regional referral hospital in rural, southwestern Uganda. Methods and findings We performed a randomized controlled trial between October, 2016 and June, 2018 at a referral hospital in southwestern Uganda. This interim analysis includes adult WLWH randomized and enrolled equally to receive a family planning voucher or standard of care (con-trol). Enrolled postpartum WLWH completed an interviewer-administered questionnaire at enrollment and 6 months postpartum. Our primary outcome of interest for this analysis is initiation of a modern family planning method within 8 weeks postpartum. Secondary outcomes included family planning initiation at 12, 14, 16, and 20 weeks postpartum, family planning discontinuation and/or change, pregnancy incidence, and mean time without contraception. The trial was registered with clinicaltrials.gov (NCT02964169). At enrollment, half of the women in both the voucher (N = 87, 55%) and control (N = 86, 54%) groups wanted to have a child in 2 years postpartum. Over 80% of referent pregnancies in the voucher (N = 136, 86%) and control (N = 128, 81%) groups were planned. All women were accessing ART. The mean CD4 count was 396 cells/mm3 (SD = 61) for those enrolled in thecontrol group versus 393 cells/mm3 (SD = 64) in the family planning voucher group. By 8 weeks postpartum, family planning was initiated in 144 (91%) participants in the voucher group and 83 (52%) participants in the control group (odds ratio [OR] 9.42; CI 4.67–13.97, P < 0.001). We also found high family planning uptake rates for both groups, with higher rates among the intervention group at 12 weeks (OR 5.66; CI 2.65–12.12, P < 0.001), 14 weeks (OR 2.51; CI 1.31–4.79, P < 0.001), 16 weeks (OR 4.02; CI 1.66–9.77, P = 0.001), and 20 weeks (OR 3.65; CI 1.40–9.47, P = 0.004) postpartum. The average time to family planning initiation was reduced to 5.9 weeks (SD = 2.4) for those in the voucher group compared to 9.3 weeks (SD = 5) in the control (P < 0.001). One pregnancy was recorded in the group receiving standard of care; none were reported in the voucher group. Method mix did not differ by group: injectables were selected by most women (N = 150, 50%), and 52% of this proportion were in the experimental arm, with <10% in each arm selecting condoms, oral contraception, or intrauterine devices (IUDs). Similar proportions of women changed contraceptive methods over the 6-month follow-up in the voucher and control groups (N = 8, 5% versus N = 5, 4%; P = 0.467). More women in the control group discontinued contraception for 1 to 2 weeks (N = 19, 13% versus N = 7, 5%; P = 0.008) or more than 4 weeks (N = 15, 10% versus N = 3, 2%; P = 0.002) compared to those given a family planning voucher. The main limitation of this study is that its findings may not be generalized to settings without improved availability of contraceptives in publicly funded facilities. Conclusion These findings indicate that a well-structured, time-bound family planning voucher program appeared to increase early postpartum contraceptive uptake and continuation in a setting in which users are faced with financial, knowledge, and structural barriers to contraceptive services. Further work should clarify the role of vouchers in empowering WLWH to avoid unintended pregnancies over time.