He attended Brooklyn Technical High School, Street.John"s College and Saint John"s Law School, and while studying worked as a telegraph messenger, as a newspaper copyboy, and wrote articles for an Italian-language paper.
He was admitted to the bar, and practiced law in Brooklyn. He was defeated for re-election in 1938, 1940 and 1941. In February 1960, he was elected as Executive Secretary of the Liberal Party in Brooklyn.
He was a Justice of the Brooklyn Civil Court from 1969 to 1973, a Justice of the New York Supreme Court from 1974 to 1981, and then an Official Referee (ie a senior judge on an additional seat) of the Supreme Court.
He died on August 8, 2003. And was buried at the Saint Charles Cemetery in Farmingdale.
DeMatteo was a member of the New York State Assembly in 1938, elected in November 1937 on the American Labor ticket in the 16th assembly district of Brooklyn.