Research shows that Buddhist precept adherence (i.e., abstaining from killing, stealing, sexual misconduct, lying, and intoxicant use) and meditation practice influence mental health outcomes. This study investigated how Buddhist precept adherence and meditation practice influenced the relationship between insecure attachment and depressive symptoms among Thai adolescents. A total of 453 Thai boarding-school students from 10th–12th grade were recruited from five boarding schools (two purposively selected Buddhist schools and three conveniently selected secular schools). They completed these tools: Experiences in Close Relationships Questionnaire—revised-18, Outcome-Inventory-21: Depression Subscale, Precept Practice Questionnaire, and Inner-Strength-Based Inventory: Meditation. A parallel mediation model analyzed the indirect effects of attachment anxiety and attachment avoidance on depression through precept adherence and meditation practice. The participants’ demographics were 16.35 ± 0.96 years, 88% female, and 89.4% Buddhist. The mean scores for attachment anxiety were 2.7 ± 1.1; attachment avoidance, 2.78 ± 1.2; overall regular precept adherence, 20.1 ± 4.4; regular but not daily meditation, 2.94 ± 1.3; and low depressive symptoms, 3.75 ± 3.4. The standardized indirect effects for attachment anxiety (β = 0.042, 95% CI = 0.022, 0.070) and avoidance (β = 0.024, 95% CI = 0.009, 0.046) on depressive symptoms through meditation and precept adherence were significant. Meditation practice had a significantly higher indirect effect size than precept adherence.