Manno was born in Alghero, Sardinia 17 March 1786 from a noble family, his father was Antonio Manno and his mother was Caterina Diaz. He moved to Cagliari, where he graduated in Civil and Canon law in 1804; in 1805 he became a tax lawyer for the Reale Udienza and in 1811 he collaborated for the realization of the magazine Foglio periodico di Sardegna, printed in Cagliari.
He moved to Turin in 1817, where he was appointed First official of the State Secretary for the Sardinian Affairs. He become the personal secretary of the King Charles Felix in 1821.
He was appointed as a member of the Supremo Consiglio di Sardegna (Supreme Council of Sardinia) in 1823, where he worked to modernize the legal system of the Kingdom. In 1826 he became a member of the Accademia delle Scienze di Torino, and in 1834 became Academic della Crusca.
On 14 October 1845, he was elected President of the Senate of Nice, and in 1847 was elected president of the Senate of Piedmont.