The name Caitlynn is a variant spelling of the Irish feminine name Caitlin or Caitlín, which is the Irish Gaelic form of the Old Celtic name Cateline. This old name is derived from the Celtic root "cad" meaning "battle" or "contention", likely referring to a quality of argumentativeness or fiery spirit. The Irish form Caitlín dates back to the late 17th century.

The spelling Caitlynn emerged in the late 20th century as an Anglicized variant, blending the Irish Caitlín with the common English suffix -lynn. This gave the name a more phonetic spelling and a feminine aesthetic that appealed to English speakers. The earliest known bearer of the Caitlynn spelling may be Caitlynn Jenner, the American former track and field athlete and television personality, born in 1949.

One of the earliest notable Caitlíns in history was Caitlín Ní Uallacháin, an Irish noblewoman who lived in the 16th century and was known as the wife of Lughaidh O'Clery, one of the principal authors of the Annals of the Four Masters. Another early bearer was the 18th century Irish harpist and composer Caitlín Nic Pháidín.

A famous literary reference is Caitlín ni Vauthier, the Irish name used by Julia M. Crottie when publishing her 1924 novel Beloved Vagabond under the pseudonym "Caitlín Ní Uaithne". There are also records of Saint Caitlín, who lived in the 6th century and established a church in Inis Cealtra, an island in Lough Derg, Ireland.

In modern times, some other notable Caitlinns and Caitlynns include Caitlynn Lawson (born 1985), a South African model and actress; Caitlynn Jenner (born 1949), the American Olympian and reality television star; and Caitlynn Jenner's daughter Caitlynn Jenner (born 1997).