Crosslinguistic influence (CLI) has emerged as a topic of interest in the field of third language acquisition (L3A) due to the increasing focus on multilingual learners. Research has considered many different issues, such as the roles of typology/psychotypology, the influence of the L2, and L2 proficiency. Thus, the present study focuses on two less-studied factors, language dominance and L3 proficiency, in the lexical CLI in the oral and written output by 52 Tagalog–English early bilinguals with Spanish as their L3. They were grouped according to their language dominance based on the findings from the Bilingual Language Profile, and according to their Spanish proficiency. The experimental tasks included a written and an oral picture description task, followed by an exit questionnaire, wherein they expressed their perception about the similarities and differences between the languages in question. Instances of lexical CLI were identified according to the classifications used in previous studies. The results suggest that language dominance is not a significant predictor of the source language of the participants’ lexical CLI production. However, the results do indicate that proficiency plays a significant role in the number and type of lexical CLI production. In other words, the number of lexical CLI produced decreased as L3 proficiency increased.