The mission of NAMI Greater Seattle is to address the unmet needs of individuals with mental illness and their families through advocacy, public education, information and referral, and self-help support groups. The NAMI Greater Seattle By-laws (Article I, Section 1) specify that the purposes of the organization are to:

1. Serve as advocates of people with chronic mental illness or severe psychiatric disabilities, regardless of age, sex, socio-economic status, or cultural heritage.
2. Provide public education and information on the need for improved direct services to people with mental illnesses.
3. Determine whether existing health care programs, systems, institutions, or laws comply with high standards of service.
4. Cooperate with and support those agencies, systems, institutions, or laws which comply with high standards of service.
5. Recommend alternatives or modifications to those programs, systems, institutions or laws which jeopardize, delay or interfere with optimum effective diagnosis or treatment of people with mental illnesses.
6. Collect and disseminate information concerning the etiology, symptoms, diagnosis, treatment and prevention of mental illness.
7. Reach out to meet the needs of families of mental illnesses through supportive crisis and referral self-help groups.
8. Act as a general resource to the community.
9. Encourage and generate funds for research and education on behalf of people with mental illness.
10. Solicit, collect, receive, hold, invest, distribute and disburse donations, subscriptions, gifts, bequests, and other funds for the purpose of the corporation.