The young Italian driver's lead in the series is now mathematically insurmountable with one event remaining on this season's calendar.
It is a third national title for the 23-year-old, who also won in 2012 and 2013.
Campani's successes also saw him take control of the Trofeo Abarth Selenia Europe series, after previous leader Niklas Lilja twice retired over the weekend.
Trofeo Abarth
Campani seals title in thrilling fashion at Monza
15/11/2014 AT 00:40
On the same weekend, young Finn Jusso Pajuranta won the European title for Abarth 500 Assetto Corse’s series.
In race one, polesitter Luca Anselmi kept the lead for less than a lap before he was overtaken by Lilja and Campani. That pair battled it out until the Swede was forced to pull out.
Manuel Buffoli took advantage to claim second, while Emanuele Moncini came in third. Anselmi had to settle for fourth.
Anselmi started well in race two and was shadowed closely by Lilja until lap six when the two cars made contact in the chicane and both drivers were forced to retire.
Buffoli took over the lead of the race, followed by Campani and Moncini before Campani made his move on the penultimate lap to seal victory.
The final event of the season takes place at Monza on October 26.
Trofeo Abarth
Lilja sets up thrilling finale with race one win at Monza
26/10/2014 AT 10:30
Trofeo Abarth
Lilja grabs pole at Monza
26/10/2014 AT 10:08