He played professionally for Italian club Bologna F.C. where he was the league top scorer (capocannoniere) in Bologna’s 1964 Serie A championship winning season.
Harald Nielsen played 14 games for the Denmark national football team in 1959 and 1960, scoring 15 goals, and he was known as Guld-Harald (Gold-Harald).
He was a football entrepreneur having continuously worked for the professionalization of both the Danish national team and the national league.
Harald Nielsen was born in Frederikshavn and started his footballing career in hometown club Frederikshavn fI, where he debuted in the second best Danish league in March 1959.
From his position of center forward, Nielsen finished the top scorer of the league as Frederikshavn won promotion to the Danish football championship.
Harald Nielsen made his debut for the Danish national team on September 13, 1959 against Norway in Oslo, as the youngest Danish national team player ever. Only 17 years and 322 days old, he scored a single goal in the 4-2 win.
In the summer of 1960, he represented Denmark at the 1960 Summer Olympics football tournament in Rome. Denmark finished runners-up and Nielsen was the leading goals scorer of the tournament.