Masiulis started his club playing career with Statyba Jonava, in the Lithuanian Second Division (LKAL).

After a year, he moved to Žalgiris Kaunas, of the Lithuanian First Division (LKL), where he played until mid-2002.

[3] As a member of the senior Lithuanian national basketball team, Masiulis played at the 1998 FIBA World Championship, and the 1999 EuroBasket.

He was also a member of the Lithuanian team that won the bronze medal at the 2000 Summer Olympic Games.

He then became an assistant coach with the club's senior men's team, Žalgiris Kaunas, in 2018.