Vasileiadis was born in Thessaloniki, Greece, and raised in Kilkis, Greece. He started his professional career with PAOK of the Greek Basket League. He was the team captain of PAOK, and he played there for 6 years, from 2000 to 2006. He had an outstanding start to his career with the club, before joining Málaga of the Spanish League. Vasileiadis was a famous and popular player while he played with the Spanish giants Málaga during the 2006–07 season. The Spanish side was able to make an impact in European competitions, partly due to the play and efforts of Vasileiadis, while he was a member of the club. The fans of the club say that he will always be remembered and appreciated by them for his efforts and play for the team on the court. On July 12, 2007, he signed a contract with the Greek EuroLeague giants Olympiacos, despite them being rivals to his personal favorite club and previous team, PAOK. He helped Olympiacos to a second-place finish in the Greek League during the 2007–08 season. Vasileiadis returned to PAOK for the 2008–09 season, as part of the club's revitalization movement under new ownership, after a previously poor 2007–08 season for the club. He was once again made the team's captain. Before the 2008–09 season was over, he moved the Italian League club Sutor Basket Montegranaro. He signed a contract with the Spanish ACB League team Obradoiro CAB in August 2009. In 2010, he signed a 3-year contract with the Spanish club Bilbao Basket, with the third year being optional. He was named to the All-EuroCup First Team in 2013. On July 19, 2013, Vasileiadis signed a contract with the Turkish League team Anadolu Efes. On August 27, 2014, he signed a two-year deal with Unicaja Málaga. He left Málaga after one season. In 2015, Vasileiadis returned home to play for PAOK Thessaloniki. With PAOK, Vasileiadis played through the Greek League's playoff quarterfinals against AEK Athens, where PAOK lost the series 2 games to 1. During the season, he averaged 14.7 points, 5.3 rebounds, and 2.1 assists per game in the Greek League, and 13.4 points and 4.8 rebounds per game in the EuroCup. At the end of the season, he rejoined Obradoiro, and played their until the end of the Spanish League season. On June 17, 2016, he signed a two-year deal with AEK Athens. On July 24, 2017, he parted ways with AEK. On October 10, 2017, he joined Aries Trikala of the Greek Basket League. On December 5, 2017, he left Trikala and signed with Iberostar Tenerife for the rest of the 2017–18 ACB season. On July 15, 2018, he signed a two-year deal with Monbus Obradoiro of the Liga ACB. On July 16, 2020, Vasileiadis and Obradoiro parted ways and his third stint with the Spanish club officially ended.