A human rights defender or human rights activist is a person who, individually or with others, acts to promote or protect human rights. They can be journalists, environmentalists, whistleblowers, trade unionists, lawyers, teachers, housing campaigners, participants in direct action, or just individuals acting alone. They can defend rights as part of their jobs or in a voluntary capacity. As a result of their activities, human rights defenders (HRDs) are often subjected to reprisals including smears, surveillance, harassment, false charges, arbitrary detention, restrictions on the right to freedom of association, physical attack, and even murder. In 2020, at least 331 HRDs were murdered in 25 countries. The international community and some national governments have attempted to respond to this violence through various protections, but violence against HRDs continues to rise. Women human rights defenders and environmental human rights defenders (who are very often indigenous) face greater repression and risks than human rights defenders working on other issues.

In 1998, the United Nations issued their Declaration on Human Rights Defenders to legitimise the work of human rights defenders and extend protection for human rights activity. Following this Declaration, increasing numbers of activists have adopted the HRD label; this is especially true for professional human rights workers.