Rapid urban expansion in the Philippines has intensified the pressure on agricultural lands, raising concerns about national food security and environmental sustainability. This study presents a national-scale spatial analysis of agricultural land conversion to built-up areas between 2003 and 2019, using high-resolution Earth Observation (EO) maps. The map validation based on expert-labeled reference data yielded 81% user accuracy, while correlation and bivariate mapping revealed a strong relationship (r 0.89) between cropland loss (ha) and built-up expansion (ha), with hotspots identified in Central and Southern Mindanao, and Central Luzon. Conversions showed a moderate association with agricultural land area (r 0.38), which may correspond to provinces with large areas for high-value crop production with intact economic value. Around 31% (3,228 out of 10,397 ha) of converted cropland to built-up fell within legally protected zones under the Network of Protected Areas for Agriculture and Agro-Industrial Development (NPAAAD), indicating possible governance and enforcement gaps. Almost 80% of the conversions within NPAAAD are mostly agro-industrial and alluvial lands characterized as high-value and road-accessible, thus being vulnerable also to urban and industrial projects. The findings underscore the urgency of enacting the National Land Use Act (NaLUA) to institutionalize spatial planning and safeguard agricultural lands from unregulated conversion. The findings of this study alongside mapping of specific land-uses following the conversions nationwide are deemed helpful inputs for mandated local land use planning.