Objective: We aimed to develop the Workplace Parent Index (WPI) as an assessment tool of family-friendly practice in the workplace and validate its psychometric properties. Methods: The development of the WPI included three phases: item generation, scale construction, and field testing. Participants were 1000 parents, aged 18 or more years old, who completed the WPI online and measures of competency of parentship, life satisfaction, and positive growth after experiencing a traumatic event. Results: The WPI comprised 80 items and five domains: Governance and Infrastructure, Planning and Communications, Action-Pregnancy and Childbirth, Action-Childrearing, and Monitoring and Feedback. All subscales of the WPI demonstrated high internal consistency reliability and correlated with other scales as expected in support of concurrent and predictive validity. Conclusions: The WPI demonstrated excellent psychometric properties that can be used to assess comprehensive family-friendly practices in the workplace when addressing the need and prioritizing the allocation of resources for workplace parentship program initiatives.