Hermes Ernesto da Fonseca (September 2, 1824 – February 7, 1891) was a Brazilian military officer and politician.

Although brother of the new president, it took him along to join the new regime, only accepting it after news of the departure of the Brazilian imperial family to Europe.

He was an amateur musician, having composed sacred and military songs (such as Polca do Regimento and mazurca Icamacuá).

Bahia was one of the last states to join the new regime, succeeding several intervenors who, due to the unstable climate, did not last in the post.

He ruled Bahia from April 26 to September 14, 1890, a period in which he sought to calm tempers and consolidate the institutions of the new regime.