Cathleen is a feminine given name that originated as an anglicized form of the Irish Gaelic name Caitlín. The name Caitlín itself is a diminutive or pet form of the Gaelic name Caitríona, which is derived from the older Irish name Cathair, meaning "battle" or "contest".

The name Cathleen first emerged in the late 16th century in Ireland, where it was used as an English equivalent to the Irish Caitlín. It gained popularity in the 17th and 18th centuries, particularly among Irish Catholics and those of Irish descent.

One of the earliest recorded examples of the name Cathleen can be found in the 17th-century Irish poetry of Dáibhí ÓBruadair, a prominent poet of the Irish bardic tradition. In his poem "Caitilín Ní Uallacháin", he celebrated the beauty and virtues of a woman named Cathleen O'Nolan.

Throughout history, several notable individuals have borne the name Cathleen. One of the most famous was Cathleen Ni Houlihan (born c. 1500), a legendary figure in Irish mythology who personified Ireland and inspired Irish nationalism.

Another notable Cathleen was Cathleen Countess of Longford (1920-2009), an English writer, historian, and philanthropist known for her biographies and her advocacy for prison reform. She was a close friend of the playwright George Bernard Shaw.

Cathleen Nesbitt (1888-1982) was a British actress who had a long and successful career on stage and screen, appearing in films such as "The Lady Vanishes" and "Whisky Galore".

Cathleen Synge Morawetz (1923-2017) was a Canadian-American mathematician and pioneering researcher in the field of partial differential equations. She was the second woman to receive the prestigious National Medal of Science in the United States.

Cathleen Blackburn (born 1950) is a Canadian environmental activist and lawyer who has been a prominent advocate for the protection of British Columbia's old-growth forests and the rights of indigenous peoples.