He started his career with Statyba Jonava in the second Lithuanian league (LKAL), however in a year he moved to Žalgiris Kaunas, where he played until mid-2002. Later he moved to Montepaschi Siena. After finishing the season with this club, he moved to Asseco Prokom Gdynia. At of the end of 2007–2008 season, after the change of club owners, Masiulis was fired and he was seriously considering the end of his career. However, after some of Žalgiris Kaunas players sustained injuries, Masiulis joined Žalgiris Kaunas again. The contract with Žalgiris Kaunas, which ended on December 16, 2008 was not prolonged, so Masiulis signed a contract Aisčiai Kaunas on December 17, 2008. After the New Year he prolonged the contract up to the end of the season.