The name Shamus is derived from the Irish Gaelic name Séamus, which is the Irish form of the name James. The name James itself comes from the Late Latin name Iacomus, which is a Latinized form of the Hebrew name Ya'aqov, meaning "supplanter" or "one who follows".

The name Séamus first appeared in Ireland in the Middle Ages, as a Gaelic form of the name James. It was particularly popular among Irish Catholics, as Saint James the Great was one of the patron saints of Ireland.

One of the earliest recorded examples of the name Shamus can be found in the Annals of Ulster, a chronicle of medieval Irish history. The entry for the year 1165 mentions a man named "Séamus Ua Cairill", who was the King of Airgialla (a medieval kingdom in modern-day Northern Ireland).

Throughout history, there have been several notable figures who bore the name Shamus or its variants. For example, Séamus Heaney (1939-2013) was an Irish poet, playwright, and Nobel laureate, widely regarded as one of the greatest poets of the 20th century.

Another famous Shamus was Séamus Ó Néill (1714-1811), an Irish harper and composer who is considered one of the last great practitioners of the ancient Irish harp tradition.

In the 16th century, Séamus mac Piarais (c. 1570-1601), also known as James McPierce, was an Irish chieftain and leader of the O'Byrne clan during the Nine Years' War against English rule in Ireland.

In the realm of literature, Séamus O'Kelly (1881-1918) was an Irish writer and poet who published several collections of poetry and short stories in the early 20th century.

Lastly, Séamus Ó Duibhir (1890-1949), better known as Séamus O'Dwyer, was an Irish language scholar and lexicographer who played a significant role in the preservation and promotion of the Irish language.