Giannattasio was an engineer by profession and a leading member of the Uruguayan Blanco (National) Party.
He became President of the body in 1964, succeeding his National Party colleague Daniel Fernández Crespo.
Prominent members of his Administration included Health minister Aparicio Méndez, who later served as President of Uruguay.
In 1965 Giannattasio died in office shortly after attending in official capacity the funeral in London, England, of Winston Churchill.
Among the prominent Uruguayan buildings for which Giannattassio's engineering company (Giannattasio & Berta, afterwards Ingeniería Civil) was responsible is the main building of The British Schools of Montevideo, Carrasco, opened 1964, as well as the main branch of Banco de la República, Av.