Nitric oxide (NO) inhibits vascular contraction by activating cGMP-dependent protein kinase I-α (PKGI-α), which causes dephosphorylation of myosin light chain (MLC) and vascular smooth muscle relaxation. Here we show that PKGI-α attenuates signaling by the thrombin receptor protease-activated receptor-1 (PAR-1) through direct activation of regulator of G-protein signaling-2 (RGS-2). NO donors and cGMP cause cGMP-mediated inhibition of PAR-1 and membrane localization of RGS-2. PKGI-α binds directly to and phosphorylates RGS-2, which significantly increases GTPase activity of G_q, terminating PAR-1 signaling. Disruption of the RGS-2–PKGI-α interaction reverses inhibition of PAR-1 signaling by nitrovasodilators and cGMP. Rgs2^−/− mice develop marked hypertension, and their blood vessels show enhanced contraction and decreased cGMP-mediated relaxation. Thus, PKGI-α binds to, phosphorylates and activates RGS-2, attenuating receptor-mediated vascular contraction. Our study shows that RGS-2 is required for normal vascular function and blood pressure and is a new drug development target for hypertension.