Born in Civitanova Marche, Pacini started his career at Marina Picena, Porto Sant'Elpidio.
[7] In July 2011 Pacini left the reserve for his first professional team Fondi, where he met his future Parma teammate Zsolt Tamási, Luigi Palumbo and Abel Gigli.
[8] Pacini made 10 starts in 23 league appearances in 2011–12 Lega Pro Seconda Divisione.
It saw Pacini along with reserve teammate Alessandro Iacobucci and first teamer Andrea Rossi and Gonçalo Brandão were exchanged with Abdou Doumbia, Alberto Galuppo, Manuel Coppola and Paolo Dellafiore.
After the bankruptcy of Siena in July 2014, Parma acquired Rossi and Pacini outright, as well as Coppola and Dellafiore became free agent.