This article aims to explore the role of eligibility for parental leave as a determinant of access and as an enabler of leave take-up. To analyse the link between eligibility and take-up, we study a unique policy change in Luxembourg's parental leave scheme. The country's 2016 parental leave reform relaxed the eligibility criteria to enable marginal part-time working parents to access the parental leave scheme for the first time. We focus on this change and examine to what extent relaxing the eligibility criteria translated into increased take-up by the marginal part-time working parents who became eligible. To quantify this transition, we analyse trends in and patterns of eligibility for the scheme in Luxembourg between 2009 and 2018 among first-time parents working full-time, part-time, or marginal part-time hours. We use a subsample of Luxembourg-resident, cohabiting, first-time parents (N = 6,254) drawn from the social security data. Our analysis shows that as eligibility is dependent on individual factors, it has similarities among mothers and fathers, whereas take-up is notably greater for mothers. After the reform, we observe that marginal part-time working mothers started taking parental leave, but up to 2018, the reform's outreach to marginal part-time working fathers remained limited. We also find that foreign national parents are less likely to be eligible for parental leave and have lower take-up rates. Despite the gendered parental leave take-up behaviours in parallel with international evidence, marginal part-time working mothers' positive response to the reform indicates progress towards strengthening women's labour market attachment in Luxembourg.