Farinacci defended Beatrice Cenci who was accused of killing her father in the most famous criminal case of the time.

He went on to become Giureconsulto e Procuratore Fiscale della Camera Apostolica (Consulting Jurist and Tax Attorney for the papal Treasury) under Pope Paul V. Along with this eminence, he was also a notoriously difficult character with quite a checkered private life.

Whilst he was a staunch prosecutor of sodomites, in 1595 he was himself accused of sodomy with Bernardino Rocchi, a sixteen-year-old page in the Palazzo Altemps, the house of his benefactor.

Farinacci was perhaps most famous as the advocate in the scandalous trial for murder, actually patricide, of Beatrice Cenci and her relatives (1599), which ended in their gruesome public beheadings.

He played a major role in the defense and although he was not able to save the girl, he did convince the pope to allow the youngest brother, Bernardo, to survive, invoking both the boy's young age and temporary mental infirmity as mitigating factors.