The court ruled that the law, which grants immunity from prosecution to the prime minister, the president and the two speakers of parliament while they are in office, is unconstitutional.
"Nothing will happen, we will go forward," Berlusconi told reporters in front of his residence in Rome on Wednesday.
"The trials they will hurl at me in Milan are real farces," he said. "I will detract some hours from taking care of the government to go there and show them to be liars."
Berlusconi said he felt "invigorated" by the challenge and defiantly ended by shouting "Long live Italy! Long live Berlusconi!"
The Constitutional Court's 15 judges made the decision after two days of deliberations. The court's ruling cannot be appealed. As a result, the Milan proceedings are expected to resume.
Berlusconi, a billionaire businessman-turned politician, has a history of legal troubles stemming from his private interests.
His conservative allies spearheaded the immunity bill through parliament last year, saying it was necessary to spare Italy's top office-holders from politically motivated persecution. Critics said it was tailor-made to spare Berlusconi from trial.
At the time the law was passed, Berlusconi was on trial in Milan, accused of corruption for allegedly bribing a lawyer to give false testimony at previous corruption trials in the 1990s.
The trial was suspended, pending review by the court. Berlusconi has denied the corruption charges.