The past several decades have seen a surge of research on nonprofit advocacy and lobbying. Previous studies have predominately focused on direct-service nonprofits, with little attention being paid to nonprofit infrastructure organizations (NIOs) that conduct advocacy on their behalf. Since advocacy and lobbying have become highly “specialized and institutionalized,” there is a pressing need to better understand the role of professional advocacy services carried out by NIOs. The present study examines NIOs’ advocacy effectiveness through the lens of absorptive capacity that highlights the importance of an organization’s capability to acquire, assimilate, transform, and exploit information toward accomplishing organizational missions. Taking advantage of an original online survey of U.S.-based NIOs, this study confirms that an organization’s absorptive capacity, including its connectedness, knowledge, and learning mechanism, influences different aspects of advocacy effectiveness.