Background and Objective: There is no comprehensive instrument for the assessment of postpartum quality of life (QOL). This study was conducted to develop the Maternal Postpartum Quality of Life Instrument (MPQOLI) and assess its psychometric properties.Materials and Methods: This methodological study was conducted in 2019–2020 using an exploratory sequential mixed-method design. A qualitative study and a literature review were conducted to generate MPQOLI items. Through purposeful sampling, 590 postpartum women were recruited to respond the instrument. Face and content validity were assessed qualitatively and quantitatively and construct validity was assessed through exploratory and confirmatory factor analyses and convergent and discriminant validity assessments. Reliability was also assessed through different methods, including Cronbach’s alpha and McDonald’s Omega.Results: Eight items were deleted in content validity assessments and eighteen items were deleted in item analysis. Participants responded the 31-item MPQOLI. During exploratory factor analysis, fifteen items were deleted and the remaining sixteen items were loaded on five factors labeled perceived support, sexual relationship, bonding with newborn, breastfeeding and newborn care, and satisfaction with postpartum transition. These five factors explained 53.26% of the total variance. Confirmatory factor analysis confirmed the five-factor structure of MPQOLI with a CMIN/DF of 2.192, an RMSEA of 0.057, a χ2 of 206.087, a PCFI of 0.738, a PNFI of 0.705, a CFI of 0.942, and an IFI of 0.943. Average variance extracted was more than 0.5 and more than maximum shared squared variance, confirming convergent and discriminant validity, respectively. Reliability was also confirmed with Cronbach’s alpha values of 0.70–0.907 and an intraclass correlation coefficient of 0.919.Conclusion: The sixteen-item MPQOLI is a valid and reliable instrument for postpartum QOL assessment. It includes items on the different aspects of postpartum QOL and can be used for the early diagnosis of impaired postpartum QOL. Further studies are needed to assess the psychometric properties of MPQOLI in different cultures and communities.