Mathias Nadeau (February 21, 1838 – February 6, 1919) was a farmer, merchant and political figure in New Brunswick, Canada.
He represented Madawaska County in the Legislative Assembly of New Brunswick as a Conservative member from 1882 to 1886.
He was born in Saint-Hilaire, New Brunswick and educated at Sainte Anne's College.
In 1862, he married Adelaide Saucier.
Nadeau was a justice of the peace and served on the county council for six years.
He was elected in an 1882 by-election held after P.