He was born in Perugia, son of Filippo Vassalli, a famous lecturer and lawyer. During World War II Vassalli was imprisoned by Nazi forces in Rome and subjected to torture. Pope Pius XII intervened personally on his behalf and was able to have his life spared 
Although in his later years Vassalli retired from public life, he was sometimes asked for his advice. During 2001 Prime Minister Silvio Berlusconi sought his advice over the European Arrest Warrant and Vassalli answered that it was a violation of the principles of natural justice.