Garlic (Allium sativum L.) is an important Philippine crop, valued both as culinary ingredient and as alternative medicine. Its bioactivity is mainly attributed to organosulfur compounds such as alliin and allicin, with other metabolites such as phenolic compounds also playing a role. Despite this, limited biochemical data exist on Philippine garlic varieties. This study aimed to characterize 12 garlic accessions collected from Ilocos Norte by determining their alliin content and total phenolic content (TPC). Alliin was quantified through high-performance thin-layer chromatography (HPTLC) densitometry, while TPC was measured using the Folin-Ciocalteu assay. Results revealed differences in both alliin content and TPC, with “Ilocos Pink” consistently exhibiting the highest values (32.84 mg/g FW of alliin; 0.4985 mg GAE/g FW of TPC), suggesting strong potential for bioactivity. In contrast, “Miracle” (19.78 mg/g FW of alliin; 0.1806 mg GAE/g of TPC) and Tan Bolters (20.07 mg/g FW of alliin; 0.1658 mg GAE/g of TPC) had the lowest values for both alliin content and TPC. These findings highlight the varietal differences among accessions, providing a baseline for further studies on their bioactivity, breeding, and post-harvest utilization. This research underscores the importance of characterizing local garlic varieties to strengthen their competitive value and to promote their utilization in specialized applications.