Giovanni Frau was born in Orroli, Sardinia, Italy, on 29 December 1890. He was born into a family of farmers and from his early youth he worked in the fields, usually about twelve hours every day.
At the age of 26, he was drafted and fought in World War I, joining the Sassari brigade among whose ranks he served in Dalmatia (present-day Croatia). Later in life, he was honored for his service with the Order of Vittorio Veneto.
In 1927, he married Giuseppa Cavalleri, with whom he had eight children. He worked as a farmer for the rest of his life, working in his garden until the age of 95. His wife died in 1995 at the age of 90.
Frau died in Cagliari, Sardinia, Italy, on 19 June 2003, at the age of 112 years, 172 days. He was survived by two sons and one daughter.
On 3 January 2002, following the death of 112-year-old Antonio Todde, he became the oldest living man in Italy.
On 14 May 2003, following the death of 113-year-old Teresa Fumarola of Apulia, he became the oldest living person in Italy.
At the time of his death, he was the fourth-oldest living man in the world (behind Yukichi Chuganji, Joan Riudavets Moll and Fred Hale), and the second-oldest validated Italian man ever.