This study examines the heterogeneous labour market effects of family leave policies for single and partnered mothers. Longer family leave has been shown to weaken women’s labour market positions and some studies have found heterogeneous effects across population groups. However, whether the effect differs by partnership status remains unexplored. Using Finnish register data from 1989 to 2014 (ca. 2.5 million person-years) and controlling for selection into single motherhood by comparing estimates from OLS and FE models, this study compares single and partnered mothers’ unemployment and earnings consequent to extended family leaves. In line with predictions that single mothers may face greater work-family reconciliation issues or cumulative disadvantage leading to greater labour market penalties, the results showed that longer leave increases the length of unemployment for single mothers more than for partnered ones. This is not solely because of selection into single motherhood. Earnings penalties after family leave (net of employment status) are the same for single and partnered mothers. We conclude that similar long- lengths of family leave are penalised more among single mothers in terms of employment, which increases and reproduces social inequalities. This means that existing inequalities are reinforced by labour market absences supported by leave policies.