The objective of this study was to determine the socioeconomic inequalities and factors associated with the use of modern contraceptive methods (MCM) in the population of sexually active women of childbearing age in Ecuador. This was an analytical observational study, based on a secondary data analysis of the 2018 National Health and Nutrition Survey (ENSANUT). Information on 19,106 sexually active, married, or cohabiting women between the ages of 15 and 49 were included. Concentration curves (CC) and Erreygers concentration indices (ECI) were calculated, taking into account the use of MCM as the dependent variable and the wealth index as the independent variable. Crude and adjusted prevalence ratios with 95% confidence intervals were calculated using generalized linear models of the Poisson family. We found that 92.8% of the women surveyed used some type of MCM in the last month. A higher educational level presented a significant pro-rich concentration in the use of MCM (EIC: 0.05; p = 0.004). On the other hand, women belonging to the age group of 20 to 29 years (ECI: −0.027; p = 0.027), women with no job (ECI: −0.025; p = 0.004), and non-indigenous women (EIC: −0.031; p < 0.001), presented a pro-poor concentration. Factors significantly associated with MCM use were age, marital status, occupation, parity, ethnicity, area of residence, and living on the coast. In Ecuador, there are socioeconomic inequalities at different levels of population subgroups in women of childbearing age. Measures to promote the use of MCM are required, focusing on groups that present inequality, taking into account the factors associated with their use.