Plurilingual instruction celebrates learners’ linguistic abilities and perceives them as valuable resources. However, despite its promotion by European policies, implementing plurilingual didactics is challenging, as it is often linked to teachers’ beliefs and their own plurilingual profiles. This correlational study investigated how teaching experience, competence in third languages (L3s) and personality traits relate to trainee teachers’ beliefs about plurilingualism-inspired pedagogy. Pre-service teachers (N = 115) of English as a foreign language completed the HEXACO Personality Inventory, a custom-made questionnaire on attitudes to plurilingualism and plurilingual didactics, and a background questionnaire assessing their plurilingual competence and teaching experience. The analysis revealed that openness to experience was positively associated with appreciations of using the mother tongue in L2-English class, suggesting openness to challenging monolingual teaching norms. Conversely, honesty-humility was negatively associated with plurilingual instruction endorsement, possibly reflecting conformity to norms regarding sole L2-English use in class. Interestingly, competence in L3s did not independently predict positive attitudes to using other languages in L2 classes. However, for participants with some teaching experience, more diversified plurilingual competence predicted greater endorsement of plurilingualism-inspired pedagogy. These findings indicate that personality, competence in L3s and teaching experience jointly shape future teachers’ beliefs about plurilingual didactics.