Margaret Irwin was born in Highgate Hill, London, to Andrew Clarke Irwin and Anna Julia Irwin. She was brought up by her uncle S. T. Irwin, a schoolmaster at Clifton High School in Bristol, after her parents died. Educated at Clifton and at Oxford University, she began writing books and short stories in the early 1920s. She married children’s author and illustrator John Robert Monsell in 1929, who created the covers for some of her books.
She was known for the accuracy of her historical research, and became a noted authority on the Elizabethan and early Stuart era. One of her novels, Young Bess, about the early years of Queen Elizabeth I, was made into a film starring Jean Simmons.
As well as historical novels, Irwin wrote several ghost stories and two fantasy novels. She also completed a factual biography of Sir Walter Raleigh called That Great Lucifer . She continued writing up until her death in 1967
