Studies on the impact of international investment agreements (IIAs), including bilateral investment treaties (BITs), on foreign direct investment (FDI) inflows have been inconclusive. This paper contributes to the debate about the effectiveness of IIAs using an original database that differentiates between investment agreements according to the quality of investor protection, and which covers a wide variety of trade and investment agreements signed and ratified in the Americas. We find evidence that in the least likely case of south–south FDI flows, high‐quality international investment treaties have a demonstrable effect on foreign direct investment inflows. Moreover, international investment agreements appear to be most effective in a context of deeper economic integration. That is, they work better when they provide higher quality protection to investors and when they are combined with other preferential economic integration agreements, such as trade agreements.