Background: Parenting interventions and conditional cash transfer (CCT) programmes are promising strategies to reduce the risk of violence against children, but evidence of the effectiveness of combining such programmes is lacking for families in low- and middle-income countries with children over 2 years of age. This study examined the effectiveness of a locally-adapted parenting programme delivered as part of a government CCT system to low-income families with children aged 2 to 6 years in Metro Manila, Philippines. Methods: Participants were randomly assigned (1:1) to either a 12-session group-based parenting programme or a control group receiving usual family services ( N = 120). Participation in either service was required among the conditions for receiving cash grants. Baseline assessments were conducted in July 2017 with 1-month post-intervention assessments in January 2018 and 12-month follow-up in January 2019. Findings: One-month post-intervention assessments indicated moderate intervention effects for primary outcomes of reduced overall child maltreatment (d = -0·50 [-0·86, -0·13]), emotional abuse (d = -0·59 [-0·95; -0·22]), physical abuse (IRR = 0·51 [0·27; 0·74]), and neglect (IRR = 0·52 [0·18; 0·85]). There were also significant effects for reduced dysfunctional parenting, child behaviour problems, and intimate partner violence, and increased parental efficacy and positive parenting. Reduced overall maltreatment, emotional abuse, and neglect effects were sustained at 1-year follow-up. Interpretation: Findings suggest that a culturally-adapted parenting intervention delivered as part of a CCT programme may be effective in sustaining reductions in violence against children in low- and middle-income countries. Clinical Trial Registration Details: All assessments were parent-report (ClinicalTrials.gov: NCT03205449). Funding Information: This research was supported by UBS Optimus Foundation and UNICEF Philippines, and by the Complexity and Relationships in Health Improvement Programmes of the Medical Research Council MRC UK and Chief Scientist Office (Grant: MC_UU_12017/14 and CSO SPHSUU14, MC_UU_1201711 and CSO SPHSU11). Declaration of Interests: Dr. Ward reports grants from UBS Optimus Foundation, grants from UNICEF Philippines, during the conduct of the study; Dr. Hutchings reports I received grant funding to contribute to the design of the trial and supervision of group leaders; Lachman is the co-developer of a non-profit parenting program with the World Health Organization ‘Parenting for Lifelong Health’, under a creative commons license, and receives fees as a trainer for this; Dr. Alampay reports that she led the team that culturally-adapted the parenting program that is being evaluated in the study; Dr. GARDNER reports grants from WHO VIOLENCE PREVENTION, grants from UNICEF Thailand, grants from UBS Optimus Foundation, outside the submitted work; and I am a co developer of the programme, PLH, tested in the trial. PLH material are open access, under a creative commons licence, and I receive no fees, royalties or other compensation as a result of its testing or implementation; all other authors have nothing to disclose. Ethics Approval Statement: Ethical procedures were approved by the University of Oxford Central University Research Ethics Committee (Reference: R43041/RE001), the Ateneo de Manila University Research Ethics Committee (Reference: AdMUREC_16_014PA), and the University of Cape Town Department of Psychology Research Ethics Committee (Reference: PSY2016-041).