Its stated purpose is to raise the level of professionalism among U.S. sheriffs, their deputies and others in the fields of criminal justice and public safety.

Since its founding in 1940, NSA has been the advocacy organization for the nation's sheriffs in Washington, D.C. Its Government Affairs Division, in conjunction with the Congressional Affairs Committee, develops the Association's policy positions and represents the Association before the United States Congress, the White House, and the various federal agencies.

The NSA provides resources, technical assistance, opportunities for professional development, information, congressional advocacy, to criminal justice practitioners.

Its annual conferences provide networking opportunities, discussion, review and formation of the Association's national policy positions on critical criminal justice and homeland security issues, and training and seminars for the Nation's sheriffs and sheriff deputies.

In April 2024, the National Sheriffs' Association protested against the sale of Vista Outdoor to Czechoslovak Group.