Manuel Díaz was born in Cuba but came to the United States in 1893 to attend the Peekskill Military Academy. He received a B.A. from the University of Havana and then returned to the United States to attend Harvard University, where he received an S.B. degree from the Lawrence Scientific School. Diaz fenced foil on the Harvard team that won the Intercollegiate Fencing Association championship in 1897, took second in 1898, and won in 1899 and 1900. He also fenced in Boston area non-collegiate competitions for the Boston Athletic Association beginning in 1897. He won the US national championship in épée in April 1899 representing the Boston Athletic Association.
After graduating from Harvard Díaz did railroad and government work for a few years and then went into mining and became vice-president and consulting engineer of the Matahambre Copper Mines in Cuba. He had married an American in Boston in 1899, the month before he won the national championship, and made frequent trips between Cuba and the United States. He was living in Cuba at the time of the 1904 Olympics.
