She was born in Bow, New Hampshire and raised a Congregationalist, though she rebelled against teachings like predestination. She suffered chronic illness and developed a strong interest in the biblical accounts of early Christian healing. In 1843 she married George Washington Glover. He died about a year later, shortly before the birth of their only child, George Washington Glover, Jr. In 1853 she married Dr. Daniel Patterson. In the 1860s she began to explore faith-healing and associated with Phineas Quimby. His influence on her is disputed; she thought highly of him personally but ultimately disavowed his technique as more mesmerism-based than Christian. After a severe injury in 1866 she turned to the Bible, recovered unexpectedly, and devoted the next three years to biblical study and the development of Christian Science. Convinced that illness was at base a mental illusion that could be healed through a clearer perception of God and of man as His spiritual idea, she began teaching her healing methodology to others privately. She divorced her second husband in 1873 for reason of adultery. In 1877 she married Asa Gilbert Eddy. She founded the Church of Christ, Scientist in Boston in 1879. Her third husband died in 1882. She devoted the remaining years of her life to the establishment of her church and revision of its textbook, Science and Health with Key to the Scriptures.
She founded the Christian Science Monitor, a non-denominational daily newspaper; the Christian Science Journal, a monthly magazine written primarily for members; the Christian Science Sentinel, a weekly religious periodical written for a wider audience, and the Christian Science Herald, a religious magazine in non-English languages.
The definitive biography is Robert Peel's trilogy Mary Baker Eddy: The Years of Discovery, Mary Baker Eddy: The Years of Trial, and Mary Baker Eddy: The Years of Authority. A more recent single volume is a 1999 work by Gillian Gill, which includes review of the numerous other biographies over the years.