He learned latin percussion first when he was a teenager, and then switched to flute. Valentin's teacher, the legendary Hubert Laws, suggested that he not double on saxophone because of his attractive sound on the flute. He studied at the Bronx Community College. In 1977, he made his recording debut with Ricardo Marrero's group and he appeared also on a Noel Pointer album. Discovered by Dave Grusin and Larry Rosen, Valentin was the first artist signed to GRP Records, and he has been a popular attraction ever since. Valentin has recorded over 15 albums, combining the influence of pop, R&B and Brazilian music with Latin and contemporary jazz to create a slick and accessible form of crossover jazz.
In 2000, he appeared in the documentary film, Calie 54, performing with Tito Puente. He toured with El Negro and MioSotis. Since the mid-2000s, Valentin has been signed to Highnote Records, releasing World On A String (2005) and Come Fly With Me(2006). He has done several collaborations with pianist Bill O'Connell, and was a Grammy Award winner for his Caribbean Jazz Project in the early 2000's with Dave Samuels as well as a Latin Grammy Award nominee in 2006.
In 2012, he suffered a stroke following a performance at the Jazz Kitchen in Indianapolis, In.