Ms. Smith is an enrolled Shinnecock, and an attorney, educator, dispute resolution professional (consulting on policies and procedures and serving as a mediator and arbitrator in various types of community, family and workplace disputes), and an advocate for health and justice, especially in the areas of racial/ethnic and gender bias prevention and intervention, and economic and environmental justice. Marguerite maintains her residence on the Shinnecock Indian Reservation on Eastern Long Island, New York, and has been instrumental in advancing various Native rights, economic development, cultural preservation and health promotion efforts of her Native Nation and others. She maintains a law practice based in Suffolk County.

She has been a member of the Board of Directors of the First Nations Development Institute since the mid-1980's and serves as one of its representatives on the Board of First Nations Oweesta Corporation. In addition to work on tribal recognition and resource rights, and supporting health care and Indian family wellness (including ICWA administration and Family Violence controls) and economic development on her reservation, she is active also in other community groups on and off reservation, including SAMP (the Shinnecock Substance Abuse Mobilization Project), Self-Development of People (a grant-making activity of the Long Island Presbytery), the South Fork Community Health Initiative, and is, in 2006, President of the Board of Directors for her county's cooperative extension service, the Cornell University Cooperative Extension Association of Suffolk County. She tries to save time to be a good daughter, sister, wife, "stepmom and grandma", and to many, "auntie"!