Acacio Gabriel Viegas (1 April 1856 – 21 February 1933) was a Portuguese physician who was credited with the discovery of the outbreak of bubonic plague in Bombay, in 1896.

Viegas was also a member of the Bombay University Syndicate, and was the pioneer of the Faculty of Scientific Technology.

Viegas correctly diagnosed the disease as bubonic plague and tended to patients at great personal risk.

With his diagnosis proving to be correct, the Governor of Bombay invited W M Haffkine, who had earlier formulated a vaccine for cholera, do the same for the epidemic.

After his death in 1933, a life-size statue of him was erected in the Cowasji Jehangir Hall opposite Metro Cinema on his birth centenary in 1956, by the Governor of Bombay Presidency, Harekrushna Mahtab, as a tribute to the services rendered to the city.