Daniel started fencing at the age of ten and during his teenage years he met famous Romanian coach Ladislau Rohonyi, who helped him become a national champion and member of the Romanian National Saber Team. Daniel Costin earned his coaching degree at the National Institute of Physical Education and Sports in Bucharest, Romania. After retiring from competitive fencing Daniel became the head coach of the Romanian Olympic Center for Juniors. Between 1989 and 1992 Daniel coached the Romanian Saber Olympic Team. Some of his notable Romanian students at the time are Vilmos Szabo, Dan Gaureanu and Daniel Grigore (members of Romanian Olympic team in Barcelona, 1992 and Atlanta, 1996). Many of his Romanian students continued their careers in fencing becoming coaches themselves. They are teaching in several European countries, Australia and North America.

In the United States Daniel continued developing his coaching skills and in 2001 he became a coach on the US Junior Saber Team, gold medalist winners of the World Championships in Gdansk, Poland. His most remarkable US students are Olympic silver medalist Jason Rogers, Beijing 2008, and national champions Teddy Levitt, Harry Mahaffey, Eric Arzoian and Alex Rey Palabrica. Daniel also coached the men’s saber team who won the 2006 US National Junior Championships and the 2007 US National Senior Championships. For about 8 years Daniel helped the US Men’s Saber Team in the Olympic qualifying process by traveling with the team to many competitions around the world. Daniel has dedicated more than 30 years to his career so far.