He was taught the sport of fencing by his father and first became the individual Italian épée champion in 1936, a title that he would claim again in 1938, 1940, 1946, 1951, and 1953. He accumulated a total of seven medals in the team épée events at the FIE World Championships in Fencing: four gold (1937, 1949, 1950, 1953), one silver (1951), and two bronze (1938, 1947). He also won a gold medal in the individual épée event in 1949 and a bronze in the same competition in 1950.[2] At the 1948 Summer Games in London, he won a silver medal in the team épée event after the Italian team finished as runners-up to France.[1] He competed at the 1951 Mediterranean Games where he won a gold medal in the team épée event.[3] At the 1952 Olympics in Helsinki the Italian team won the gold medal, and Mangiarotti won an additional silver medal in the individual épée competition, finishing behind his brother Edoardo.[1] He won his final title at the 1966 World Masters Championships in Rome in the individual épée category.[4]
In 1967 he took up the position of Head Maestro of the Italian fencing school Circolo della Spada, a position that he still held as of his 90th birthday in 2005. His niece Carola is also an Olympic fencer who competed in the 1976 and 1980 editions of the Games. Another brother, Mario, was also a fencer before he retired from the sport to become a cardiologist.[2] He died on 9 April 2010 in Lavagna, at the age of 94.[5]