Mary Sue Hubbard
- Category : 1931-births
- Type : MGE
- Profile : 4/6 - Opportunistic / Role Model
- Definition : Split - Small (10,33,45)
- Incarnation Cross : RAX Eden 2
American leading figure in Scientology, who was the third wife of L. Ron Hubbard, from 1952 until his death in 1986. The Hubbards had four children; Diana (born 1952), Quentin (1954-1976), Suzette (born 1955), and Arthur (born 1958).
She became involved in Hubbard's Dianetics in 1952, while still a student at the University of Texas at Austin, becoming a Dianetics auditor. She soon became involved in a relationship with Hubbard and married him in March 1952. She accompanied her husband to Phoenix, Arizona, where they established the Hubbard Association of Scientologists – the forerunner of the Church of Scientology, which was itself founded in 1953.
She was credited with helping to coin the word "Scientology". She played a leading role in the management of the Church of Scientology, rising to become the head of the Church's Guardian's Office (GO).
In August 1978, she was indicted by the United States government on charges of conspiracy relating to illegal covert operations mounted by the Guardian's Office against government agencies. She was convicted in December 1979 and was sentenced to five years' imprisonment and the payment of a $10,000 fine. She was forced to resign her post in July 1981 and served a year in prison from January 1983, after exhausting her appeals against her conviction. In the late 1990s, she fell ill with breast cancer and died on 25 November 2002, aged 71, in Los Angeles, California.