After graduating in law from the University of Modena in 1874, he practised as a lawyer before embarking on an academic career.

Beginning as a freelance lecturer in civil procedure in Bologna in 1882, he obtained the position of extraordinary professor in the Faculty of Law of the University of Pisa in 1886 soon after he published, at the age of thirty, a pamphlet on the politics of law: The Modern State and Justice.

In 1892, together with Carlo Francesco Gabba, he took over the direction of the magazine Giurisprudenza italiana, which he continued for forty-five years.

[6] As a magistrate, Mortara dealt with all sorts of controversies; for example, during his presidency of the Court of Appeal of Ancona in 1906, he upheld the right of ten women teachers from Senigallia to be registered on the electoral lists.

[6] In 1910, Mortara was appointed to the Senate of the Kingdom of Italy, and in 1919–1920 served as minister of justice with the first Nitti government.