She was born Mary Philadelphia Watkins in
Brompton, London in 1804. Her father, Sir Charles Watkins, was a barrister who specialised in transferring property ownership. In 1826/7, she married John Merrifield Their other children were Henry born 1830, Emily born 1835 and Edward born 1836. They later moved to Dorset Gardens, Brighton. Her husband worked as a barrister and she undertook the translation of a book on painting by the 15th-century artist
Cennino Cennini. The book,
Treatise of Painting, was published in 1844. In 1846, she published
The Art of Fresco Painting, which was a commission for the
Royal Commission on the Fine Arts, being assisted by her two sons. In 1850, she exhibited her paintings in the first art exhibition held in Brighton's Royal Pavilion. In 1851, Merrifield wrote the essay
Harmony of Colours, which was published in
The Art-Journal Illustrated Catalogue of the Great Exhibition. The text formed part of the introductory essays accompanying the richly illustrated catalogue of decorative arts objects exhibited at the
Great Exhibition in London. In 1854, she chose a different subject and published
Dress as a Fine Art, which supported the more practical improvements of
Amelia Bloomer. In 1857, she was showing her knowledge of local history when she published
Brighton Past and Present. In 1857, she was honoured with a
civil list pension of £100 per year. She continued to publish papers in the British scientific journal
Nature. She also worked arranging natural history displays at
Brighton Museum and Art Gallery. ==Death and legacy==