Out-of-field teaching continues to challenge teachers who are expected to deliver quality instruction despite specialization mismatches. This study examined the relationship between out-of-field teaching competence and professional development among Technical-Vocational-Livelihood teachers in Dupax del Sur and Dupax del Norte, Nueva Vizcaya. Its importance lies in providing evidence for strengthening teacher support, instructional effectiveness, and professional growth among teachers handling subjects beyond their field of specialization. A quantitative descriptive-correlational design was used, involving thirty-one purposively selected teachers from five public secondary schools. Data were gathered through a validated four-point Likert-scale questionnaire and analyzed using mean, standard deviation, the Shapiro-Wilk test, and the Pearson product-moment correlation coefficient at the 0.05 level of significance. Results showed that respondents had a high level of out-of-field teaching competence, with classroom management receiving the highest mean and subject matter mastery showing the lowest. Moreover, professional development indicated a high level, with instructional adaptability obtaining the highest mean, and perceived career growth obtaining the lowest. The variables were normally distributed, and correlation analysis revealed a moderate, positive, and significant relationship between out-of-field teaching competence and professional development. The findings indicate that teacher competence and professional development are mutually reinforcing. The proposed Technical-Vocational-Livelihood Support for Teaching Effectiveness and Professional Growth Program may therefore serve as a school-based intervention to strengthen content mastery, instructional support, assessment practices, mentoring, reflection, and career growth among teachers assigned outside their specialization.