Guerra is the son of a professional baseball player and grew up next to the National Music Gallery. As a teen, he was influenced by the Beatles and by the music of the U.S. hippies. Initially, he taught himself the basics of guitar playing, but after winning a contest, attended the National Conservatory on a scholarship. One of his instructors then helped Guerra get into the prestigious Berklee College of Music in Massachusetts and the many genres of jazz. In time, he found he missed his native Dominican Republic and so returned to experiment with blending local African-influenced music, folk songs and jazz with his group 440. The band takes its name from the universal tuning pattern of the A note, 440 Hertz. The name was chosen by Guerra's brother José Gilberto who used to sit and watch them rehearse. One day he commented that they seemed so obsessed with staying in perfect tune that they call themselves that.

Their debut album, Soplando, made little impact. For their next efforts, Mudanza y Acarreo and Mientras Más Lo Pienso Tu, Guerra and 440 began adding merengue and lightning-quick riffs of "perico ripiao," and suddenly found success with a young crowd tired from hearing the same old thing. The new music, called "bachata-merengue," soon won considerable acclaim in the Dominican Republic and were selected by their government to represent the country in the International Music Festival of OTI, the Oraganization of Iberoamerican Television. In 1988, Guerra and 440 had one of their biggest hits, Ojalá Que Llueva Café, which became the third best-selling album in Latin America. That year he lost his lead vocalist, Maridalia Hernández, who left to pursue her solo career in Europe, leaving Guerra to become the new lead singer. In 1991, he released Bachata Rose which became a smash hit throughout the Americas and won Guerra his first Grammy in the U.S. The album was particularly popular in Los Angeles and soon Guerra and his band were touring. His next album, Areito, caused controversy in the Dominican Republic for speaking out against social injustice that the desperately poor felt Guerra had never personally experienced. Still, he must be given credit for his sincerity and interest in improving things in his oft-troubled homeland. Musically, Guerra changed directions again for his 1995 effort Fogaraté. This album incorporated more of the increasingly popular African soukous music. It became quite popular.