Mello was born in New Haven, Connecticut on October 18 1960. He was the third child of James and Sally Mello. His father, James Mello, was a paleontologist and his mother, Sally Mello, was an artist. His fathers parents moved to the US from the Portuguese islands of Azores. His parents met while at the Brown University and were the first children in their families to go to college. James Mello was awarded his PhD in paleontology from Yale University in 1962. The Mello family moved to Falls Church in northern Virginia so that James could take a job with the United States Geological Survey (USGS) in Washington, DC.