Pisenti was born in Perugia, Umbria, to a family of university professors. In 1912 he graduated in jurisprudence at the University of Bologna. The following year he moved to Pordenone, Friuli, where he began his political carrier as a member of the town council, which he held from 1915 to 1919, elected on conservative list. In 1920 he founded in Pordenone the far right party Unione del Lavoro (Labour Union), which was later absorbed into the National Fascist Party (PNF).
In 1926 Pisenti was expelled from the PNF, as he disagreed on some internal regulations of the party. The following year, however, he was readmitted into high office, becoming one of Benito Mussolini's closest collaborators (Mussolini described him as "the man who, throughout twenty years of Fascism, has had the bravery of his very own brilliant heterodoxy"). In 1924 he was elected as to the Italian Chamber of Deputies, a position he held without interruptions until 1939.
After the armistice of September 8, 1943, he remained loyal to Mussolini, and joined the leadership of the Italian Social Republic - in November of that year, he was appointed its Minister of Justice. In this position, he refused to grace the former Fascist leaders who had organized the fall of Mussolini in 1943 (including Galeazzo Ciano, Emilio De Bono and Carlo Pareschi), and who were therefore condemned to death in the Verona trial because he sad that the last decision about a pardon or was a duty of the head of the state of Repubblica Sociale italiana, but other member of the fascist leadership like Pavolini refused to inform Mussolini about the request of pardon. After the end of World War II, Pisenti was arrested and jailed for a year. After the sentence was carried out, he returned to Pordenone and worked as lawyer. In 1977 he wrote the controversial essay RSI - Una Repubblica necessaria ("The RSI [Italian Social Republic] - A Necessary Republic"), in which he defended the politics of the Republic.
Pisenti died in Pordenone in 1980.