Abstract Tropical deforestation driven by agricultural expansion to meet growing food demand poses a rising threat to the global carbon cycle. While previous studies quantified agriculture‐related carbon losses, the role of cropland expansion remains poorly resolved, partly because widely used agricultural driver data sets are too coarse to detect fine‐scale forest‐to‐cropland conversion, especially in topographically complex regions. Here we integrate multiple high‐resolution satellite observations to show that tropical forest‐to‐cropland conversion reached 1.08 Mha yr−1 during 2004–2019, accelerating by 0.35 ± 0.07 Mha yr−1 per four‐year period (p < 0.05). These conversions shifted toward steeper terrains, with mean slope rising by 0.16 ± 0.05° per period. Annual forest carbon loss nearly tripled from 46 to 130 TgC yr−1, increasing at 30 ± 6 TgC yr−1 per period (p < 0.05). Our findings reveal a systematic shift of agricultural frontiers toward marginal, carbon‐rich tropical forests, underscoring the need for more targeted land‐use governance to support global climate mitigation goals.