BACKGROUND: Timely initiation of modern contraceptive use is vital to prevent unintended pregnancy and its related morbidities and mortalities. However, there is a scarcity of evidence about the duration of time elapsing from childbirth to initiating modern contraceptive use following childbirth and its associated factors in the study area for evidence-based interventions. Therefore, we aimed to assess the time to initiation of modern contraceptive method use and its predictors in Hossana town, southern Ethiopia. METHODS: A retrospective follow-up study was conducted at public health facilities in Hosanna town. A total of 503 study participants were included in the study using a systematic random sampling technique. The Box and Whisker plot was used to estimate the time to initiation of modern contraceptive use. A Weibull regression model was applied to identify predictors of time to initiation of modern contraceptive use. Adjusted Hazard Ratio (AHR) with a 95% confidence interval (CI) was used to interpret the strength of the association. RESULTS: The median time to initiation of modern contraceptive use was 6 months, with an interquartile range of 3 months. Husband/partner attending higher education [AHR = 1.64, 95% CI: 1.04, 2.57], women who had parity of more than two [AHR = 1.93, 95% CI: 1.01, 3.67], and women who had communicated with their husband/partner about modern contraceptive methods [AHR = 3.03, 95% CI: 1.41, 6.67] were more likely to initiate modern contraceptive method use within six months after childbirth. In contrast, women with an older age of greater than or equal to 30 years [AHR = 0.32, 95% CI: 0.13, 0.82] and who did not resume sexual intercourse after childbirth [AHR = 0.02, 95% CI: 0.01, 0.03] were less likely to initiate modern contraceptive method use within six months after childbirth. CONCLUSIONS: The median time to initiation of modern contraceptive method use after childbirth in the postpartum period was delayed from the World Health Organization recommendation of at most 6 weeks. Emphasis should be given to older women, women with lower parity, and men's participation in contraceptive communication to improve timing for initiation of modern contraceptive use after childbirth and to curb the five-month lag periods.