Cosimo Matassa was born in New Orleans in 1926.  In 1944 he began studies as a chemistry major at Tulane University, which he abandoned after completing five semesters of course work. In 1945, at the age of 18, Matassa opened the J&M Recording Studio at the back of his family’s shop on Rampart Street, in the French Quarter of New Orleans.  In 1955, he moved to the larger Cosimo Recording Studio on Gov. Nichols Street, nearby in the French Quarter.

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As an engineer and proprietor, Matassa was crucial to the development of the sound of R&B, Rock and Soul of the 1950s and 1960s, often working with the producers Dave Bartholomew and Allen Toussaint. He recorded many hits, including Fats Domino’s "The Fat Man" (a contender for the first rock and roll record), Little Richard's "Tutti Frutti", and records by Ray Charles, Lee Dorsey, Dr. John, Smiley Lewis, Bobby Mitchell, Tommy Ridgley, the Spiders and many others. He was responsible for developing what became known as the New Orleans sound, with strong drums, heavy guitar and bass, heavy piano, light horns and a strong vocal lead. In the late 1950s and early 1960s, Matassa also managed the successful white New Orleans rock-and-roll performer Jimmy Clanton.

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Matassa retired from the music business in the 1980s to manage the family's food store, Matassa's Market, in the French Quarter.  

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In December 1999, J&M Recording Studio was designated as a historic landmark.  In October 2007, Matassa was honored for his contributions to Louisiana music with induction into the Louisiana Music Hall of Fame. In the same year he was also given a Grammy Trustees Award.  On September 24, 2010, the Rock and Roll Hall of Fame and Museum designated J&M Recording Studio a historic Rock and Roll Landmark, one of 11 nationwide.  In 2012, he was inducted into the Rock and Roll Hall of Fame in Cleveland as a nonperformer.  He was inducted to the Blues Hall of Fame in 2013.