Charles-Antoine-Ernest Gagnon (December 4, 1846 – June 11, 1901) was a notary and political figure in Québec.

He was educated at the Collège de Sainte-Anne-de-la-Pocatière and was licensed as a notary in 1869, setting up practice at Rivière-Ouelle and later in Québec.

Gagnon also served as secretary-treasurer for the municipality and for the school board of Rivière-Ouelle.

He served in the cabinet of prime minister Honoré Mercier as provincial secretary and registrar from 1887 to 1890.

Gagnon died in Québec at the age of 54 and was buried in Rivière-Ouelle.