Italy's backcourt reigned supreme as guards Simona Ballardini and Raffaella Masciadri scored 18 points each in the win.
Masciadri made six of 10 from the field, including three of four from beyond the arc.
After a tight first quarter, Italy pulled away before half-time and took a 40-32 advantage into the locker rooms.
Laurence Val Malderen led Belgium with 15 points while Sara Leemans had 13 and Jana Raman had 10.
The win leaves Italy at 3-0 going into their final game against Croatia on Monday.
The result eliminates Belgium and makes Monday's clash between Italy and Croatia a dead rubber.
Giampiero Ticchi (Italy coach):
"I am really very happy, we worked hard in the last few months and I believe we deserve this qualification to EuroBasket. I'd like to congratulate all my players because they played three good games but it is important to remember how the Italian Federation worked to help us achieve this qualification. We will go to Latvia with this group [of players]. [Before today] Italy hasn't succeeded in a qualification [to a EuroBasket] in the last 10 years and that's a long time... "
Raffaella Masciadri (Italy player):
"A dream comes true, I've been playing in the National Team for a lot of years and finally we succeeded in a qualification. Last time I didn't play with the team because I was in the WNBA championship but in this Additional Round I found a solid team. It is a great day for our basketball, in Latvia we want to demonstrate that the Italian National Team deserves to be among the best 16 teams of Europe."