Marryat was born in Brighton, Sussex, in 1833. Her parents separated when Marryat was young; her childhood was divided between her parents' residences, where she was privately educated.

Shortly before her 21st birthday, she wed Thomas Ross Church, an officer in the Madras staff corps of the British Army in India; they spent the first seven years of their married life traveling India extensively before she returned to England in 1860. They divorced in 1879; later that year, Marryat wed Colonel Francis Lean. She had eight children with her first husband.

At the age of 43, Marryat entered the stage, taking a role in a drama she had written, Her World Against a Lie, in 1881. She died in 1899 from diebetes and pneumonia and is buried in Kensal Green Cemetery in London.

Marryat always used the name Marryat professionally, beginning with her first novel, Love's Conflict (1865), which she wrote to distract herself when her children developed scarlet fever. She published 67 more novels before her death, as well as various non-fiction works such as The Life and Letters of Captain Marryat (1872) and Gup (1868), an account of garrison life in India. There is No Death (1891) and The Spirit World (1894) give accounts of séances she attended.