Background: #Digital interventions offer a promising avenue for scalable #Parenting support in low- and middle-income countries, where in-person coverage remains limited. However, engagement disparities may reduce their potential for population-level impact. Objective: This study examined caregiver-level predictors of engagement with #ParentApp, a smartphone-based adaptation of the #Parenting for Lifelong Health (PLH) for Teens program for caregivers of #Adolescents aged 10 to 17 years. Methods: This study was nested within a cluster-randomized factorial trial of #ParentApp in Mwanza, Tanzania, implemented according to the optimization phase of the Multiphase Optimization Strategy. Clusters (n=16), comprising 614 caregivers (n=205, 33.4% men), were randomized to 3 components: guidance (guided vs self-guided), app design (unstructured vs structured), and #Digital support (enhanced vs basic). #Digitally tracked app engagement outcomes included the number of modules completed, the first module not started, and the first module not completed. Baseline candidate predictors included demographic, socioeconomic, behavioral, and psychological factors assessed via an app-embedded questionnaire. Poisson generalized linear mixed-effects models with random effects for clusters assessed associations between predictors and each outcome. Interaction terms were specified to test whether associations differed by caregiver gender. Results: Among 614 caregivers, 596 (97.1%) completed the first module; however, engagement declined rapidly thereafter, with only 281 (45.8%) completing module 2 and 49 (7.9%) completing all 12 modules. Overall, mean content completion was 35.6% (SD 33.1%) of the program. Women completed approximately 15% more modules than men (incidence rate ratio 1.15, 95% CI 1.05-1.27, =.003), despite reporting higher levels of financial stress, food insecurity, #Child maltreatment, and depressive symptoms at baseline (all ≤.02; Cohen =0.19‐0.37). No other caregiver characteristics were significantly associated with engagement. Conclusions: This is the first known study to investigate caregiver-level predictors of engagement with a #Digital #Parenting intervention in a low- and middle-income country. Engagement with #ParentApp was broadly consistent across caregiver subgroups, with the exception that women completed significantly more modules than men. To equitably engage men and fathers, future studies should pair father-inclusive, identity-affirming content with implementation strategies that reduce social and economic barriers to participation. Trial Registration: Pan-African Clinical Trial Registry PACTR202210657553944; https://tinyurl.com/yc2bmsx7 International Registered Report Identifier (IRRID): RR2-10.1186/s12889-023-15989-x