The daughter of Thomas Strickland of Reydon Hall, Suffolk, Agnes was educated by her father, and began her literary career with a poem, Worcester Field, followed by The Seven Ages of Woman and Demetrius. Abandoning poetry, she next produced, among others, Historical Tales of Illustrious British Children (1833), The Pilgrims of Walsingham (1835), Tales and Stories from History (1836). Her chief works, however, are Lives of the Queens of England from the Norman Conquest, and Lives of the Queens of Scotland, and English Princesses, etc.. (8 vols., 1850–1859), Lives of the Bachelor Kings of England (1861), and Letters of Mary Queen of Scots, in some of which she was assisted by her sister Elisabeth. Strickland's researches were laborious and conscientious, and she remains a useful source, but she failed to exercise the level of objectivity that a modern historian would aspire to. Her style is considered mediocre by some, but writing should be compared only directly to that of the contemporaries of the time. Most of the Strickland sisters' historical research and writing was actually done by Elisabeth. Elisabeth however eschewed all publicity and Agnes was put forward as author. Their biographical works are fine representations of the larger body of biographies written by Victorian women, a significant subset of Victorian biography with unique characteristics, including the focus on female subjects and inclusion of information that was more "social" in nature, such as dress, manners, and diet.
Two of Agnes's other sisters were also writers, Susanna Moodie and Catharine Parr Traill, who are famous for their works about pioneer life in early Canada, where they both emigrated with their husbands in 1832.