Dictionary of Medieval Names
from European Sources

Marmaduke m. Possibly Old Irish máel 'bald, tonsured' + Old Irish Máedoc 'of Máedoc', the name of a 6th-7th C Irish saint.

Spellings like Marmaduke were virtually restricted to North Yorkshire, England before the 16th C; if the origin of the name really is Old Irish (as Withycombe s.n. Marmaduke suggests), then this is one of the rare instances of a name which was borrowed from Irish into English, rather than the other way around.

England
Early Modern English
1557 Marmaduke PRThirsk p. 2; 1565 Marmaduke CAmar-vol1 p. 2; 1592 Marmeduke DEmar-vol1 p. 86; 1593 Marmaduke DEmar-vol2 p. 27; 1595 Maraduke CAmar-vol1 p. 5
Cite as: S.L. Uckelman. "Marmaduke". In S.L. Uckelman, ed. The Dictionary of Medieval Names from European Sources, Edition 2016, no. 4. http://dmnes.org/2016/4/name/Marmaduke.