Helen Landreth was born in Nashville, Tennessee, in 1892. Her father, Olin Landreth, was then the Dean of the Engineering Faculty at Vanderbilt University in Nashville. In 1894, the family moved to Schenectady, New York, where her father headed the Engineering Department at Union College.

In 1914, Landreth entered Teachers College at Columbia, but left in 1918 before completing her degree requirements. She joined the staff of Collier's, a magazine based in New York, in 1922. In 1925, Landreth traveled to Lodz, Poland with her father, and saw, from the ship, Ireland for the first time. This first glimpse acted as a magnet on her mind and imagination. The study of Ireland would become her life's work.

Landreth worked for a brief time as a fiction editor for McClure's magazine in New York before returning to Ireland. She devoted herself to research and writing. Her first book,Dear Dark Head, a history of Ireland until 1919, was published in 1936. She returned to Ireland in 1938 to work on her second book, The Pursuit of Robert Emmet, which was published in 1949.

While in the US to oversee publication of this book, Landreth met Rev. Terence Connolly, S.J., who was then the Librarian of Boston College and a great admirer of her work. Connolly asked Landreth to assemble an Irish Collection for Boston College and Landreth accepted.

Landreth worked in the Library's Irish Collection for the next 30 years, until her retirement in 1979. During this time, she wrote a small volume on Mary Childers, based on their correspondence, as well as writing several articles which appeared in magazines in both the United States and Ireland.

Landreth never married nor had any children. In 1964 she was inducted into the Eire Society. In 1976 she received the Boston College Bicentennial Medal. She was also a dedicated volunteer at the Children's Hospital in Boston, beginning in 1955, working mainly with polio victims. She died in 1981.