Previous studies examining the role of executive function in L2 processing show that working memory (WM) facilitates the processing of agreement in local domains in adult second language (L2) learners. Furthermore, other studies explored whether L2 learners can establish the agreement operation across phrases (i.e., structural distance) and whether WM intervenes in the said linguistic computation. However, these studies have often included both syntactic and linear distance in their stimuli, making it impossible to discern whether WM effects emerge from physical or syntactic reasons. The present study assesses how verbal WM updating and L2 proficiency modulate syntactic processing. Beginner and advanced adult English L2 learners of Spanish and Spanish monolinguals completed a verbal WM updating task, and a self-paced reading task containing Spanish sentences with gender agreement and disagreement within and across phrases. Results show that Spanish monolinguals exhibited sensitivity to gender agreement violations in local domains and in structural distance conditions, while beginner L2 learners were not sensitive to violations in either condition. Advanced learners, on the other hand, detected violations in local domains, and their verbal WM updating spans were associated with sensitivity to violations across phrases. Taken together, the findings suggest that (a) morphosyntactically complex structures consume cognitive resources in great number, and (b) L2 processing is qualitatively similar albeit quantitatively different from native processing, thus providing evidence that late bilinguals may process the L2 in a native-like manner.