Hypertension is the most common cardiovascular disease, afflicting >30% of adults. The cause of hypertension in most individuals remains unknown, suggesting that additional contributing factors have yet to be discovered. Corin is a serine protease that activates the natriuretic peptides, thereby regulating blood pressure. It is synthesized as a zymogen that is activated by proteolytic cleavage. CORIN variants and mutations impairing corin activation have been identified in people with hypertension and pre-eclampsia. To date, however, the identity of the protease that activates corin remains elusive. Here we show that proprotein convertase subtilisin/kexin-6 (PCSK6, also named PACE4; ref. 10) cleaves and activates corin. In cultured cells, we found that corin activation was inhibited by inhibitors of PCSK family proteases and by small interfering RNAs blocking PCSK6 expression. Conversely, PCSK6 overexpression enhanced corin activation. In addition, purified PCSK6 cleaved wild-type corin but not the R801A variant that lacks the conserved activation site. Pcsk6-knockout mice developed salt-sensitive hypertension, and corin activation and pro-atrial natriuretic peptide processing activity were undetectable in these mice. Moreover, we found that CORIN variants in individuals with hypertension and pre-eclampsia were defective in PCSK6-mediated activation. We also identified a PCSK6 mutation that impaired corin activation activity in a hypertensive patient. Our results indicate that PCSK6 is the long-sought corin activator and is important for sodium homeostasis and normal blood pressure.