In the current study, we examined the role of first-language (L1) influence on the additional-language development of grammatical gender marking in Spanish. The participants were L1 speakers of English or French (N = 215), who were learning Spanish and who were at three instructional levels. The data came from their use of gender marking in noun-modifier pairs in an argumentative essay. We adopted the unified methodological framework developed by Scott Jarvis and we applied insights from variationist second language acquisition to contribute to the discussion about whether learners' L1 impacts variability in targetlike gender marking in additional-language Spanish. Specifically, we designed our study to investigate four types of evidence that Jarvis identified (intragroup homogeneity, intergroup heterogeneity, cross-language congruity, and intralingual contrasts), and we used variationist methods to account for other factors that are known to impact variable use of gender marking. The quantitative analyses supported each type of evidence, consequently demonstrating that these learners' L1 influenced their variable use of gender marking in Spanish. We concluded by reflecting on the contributions that the current study has made to the understanding of gender marking in additional-language Spanish and to research on L1 influence more generally.