Julio Velasco began playing volleyball at the age of 15 for La Plata University Club. His team won the Junior Club championship in 1969 and 1970 and he was named Best Junior Player of the Year. In college, he played volleyball and coached junior teams. He coached Ferrocarril Oeste to four National Championships in 1979-1982.

He became assistant coach on the Argentinean National Team from 1981-1983. In 1983, he was invited to coach for Tre Valli Jesi in Italy, staying until 1985. He coached at Panini Modena 1985-1989 and led them to four Italian National Championships in 1986-1989.

In 1989, he was hired to coach the Italian National Men’s Team. He immediately led them to a Gold Medal at the European Championships in 1989, which his team won twice more in 1993 and 1995. The team also won a Silver Medal at the World Cup in 1989.

He de-emphasized the specialization trend of the 1980’s. He emphasized the concept of the “square”, team unity where the team was better than the sum of its players. He was meticulous, well prepared and very demanding, but he knew how to win.

Starting at the 1990 World Championships and the 1990 Goodwill Games, the Italian National team swept the world volleyball events for five years. They won a Gold Medal in the World Champion-ships in 1990 and 1994, the World League in 1990, 1991, 1992, 1994 and 1995, 1991, the Mediterranean Games, and the 1993 Grand Champions Cup. They won a Silver Medal at the Olympic Games.

Julio Velasco left the Italian National Men’s Team in 1996 to coach the Italian National Women’s Team, whom he coached to a Gold Medal at the Mediterranean Games. He coached the Czechoslovakian National Men’s Team in 2001. He returned to Italy to coach the Coprasystel Volleyball Club in 2002.

In 2011, Velasco was signed as the head coach of the Iran men's national team. He became coach of the Argentina men's national team before his contract expired with the Iranian national team on March 1, 2014.