Mary Seymour was the daughter of Katherine Parr, queen dowager of England and Thomas Seymour, Baron Seymour of Sudeley and uncle to Edward VI.

Mary Seymour may also refer to:

• Mary Somerset, Duchess of Beaufort (gardener) (1630–1715), married name Mary Seymour
• Mary Seymour, Duchess of Somerset (1697–1768)
• Mary Seymour, Marchioness of Hertford (1846–1909)
• Mary Foot Seymour (1846–1893), American writer
• Mary Townsend Seymour (1873–1957), American politician
• Mary Alice Seymour (1837–1897), American musician, author, elocutionist, and critic
• Mary Seymour (died 1886), wife of Horatio Seymour and First Lady of New York