Unintended pregnancy is a major driver of poor maternal and child health in resource-limited settings. Data on pregnancy intention and use of family planning (FP) is scarce in Papua New Guinea (PNG), but are needed to inform public health strategies to improve FP accessibility and uptake. Data from a facility-based cross-sectional sample of 699 pregnant women assessed prevalence and predictors of unintended pregnancy and modern FP use among pregnant women in East New Britain Province, PNG. More than half (55%) the women reported their pregnancy as unintended. Few (18%) reported ever having used a modern FP method, and knowledge of different methods was low. Being single, separated or divorced (AOR 9.66; 95% CI 3.27–28.54), educated to a tertiary or vocational level (AOR 1.78 CI 1.15–2.73), and gravidity > 1 (AOR 1.43 for each additional pregnancy CI 1.29–1.59) were associated with unintended pregnancy; being accompanied by a male partner to ANC was associated with a reduced unintended pregnancy (0.46 CI 0.30–0.73). Factors associated with modern FP use included male partner involvement (AOR 2.26 CI 1.39–3.67) and gravidity > 1 (AOR 1.54 for each additional pregnancy CI 1.36–1.74). FP use also varied by the facility women attended. Findings highlight an urgent need for targeted interventions to improve FP knowledge, uptake and access, and male partner involvement, to reduce unintended pregnancies and their complications.