Early coaching career In October 2009, Masiulis became a
coach at the basketball school of
Žalgiris-2, coaching the Under-14 team. In January 2010, he became an assistant coach with
Aisčiai Kaunas. He was next the
head coach of
Žalgiris-2's main team, which is the
reserve team of Žalgiris Kaunas. He led the team to the
Lithuanian Second Division (NKL) Finals in 2016 and 2018.
Žalgiris Kaunas (2018–2020) In July 2018, Masiulis joined the Lithuanian powerhouse
Žalgiris Kaunas coaching staff as an assistant coach of
Šarūnas Jasikevičius and this way replaced
Darius Songaila, who joined the
San Antonio Spurs. This was the beginning of a successful long-term collaboration of two childhood friends in the same teams coaching staff. Being a part of the Žalgiris Kaunas coaching staff, Masiulis became twice the Lithuanian League champion in the
2018–19 LKL season, and
2019–20 LKL season, as well as won the
2019–20 King Mindaugas Cup.
FC Barcelona (2020–2023) and another assistant coach
Darius Maskoliūnas coaching FC Barcelona in 2022 In July 2020, Jasikevičius became the head coach of the
FC Barcelona Bàsquet and soon Masiulis joined him as an assistant coach. The FC Barcelona Bàsquet, coached by Lithuanian coaching staff of Jasikevičius, Masiulis and
Darius Maskoliūnas, in the
2020–21 ACB season reclaimed the Spanish League champions title for the first time since
2014. Later the FC Barcelona Bàsquet also became the Spanish League champions in the
2022–23 ACB season. Nevertheless, while Masiulis was a part of the FC Barcelona Bàsquet coaching staff, the FC Barcelona Bàsquet failed to win the top-tier European basketball league
EuroLeague as in the
2021 EuroLeague Final Four they finished second, in the
2022 EuroLeague Final Four finished third, and in the
2023 EuroLeague Final Four finished fourth. Following the 2022–2023 season, head coach Jasikevičius left the FC Barcelona Bàsquet and Masiulis did so as well.
Fenerbahçe Istanbul (2023–2025) In December 2023, Jasikevičius became a head coach of the Turkish powerhouse
Fenerbahçe Istanbul and Masiulis also signed in December 2023 with the Fenerbahçe Istanbul, becoming once again an assistant coach of Jasikevičius. In the first season in the Fenerbahçe Istanbul's coaching staff Masiulis won the
2023–24 Turkish League,
2024 Turkish Basketball Cup, and finished fourth in the
2024 EuroLeague Final Four. In the
second season in the Fenerbahçe Istanbul's coaching staff Masiulis contributed to Fenerbahçe Istanbul's
European Basketball Triple Crown (won the
Turkish League,
Turkish Cup, and EuroLeague in the
2025 EuroLeague Final Four). In his debut season as head coach of the Žalgiris Kaunas he won the
2025–26 King Mindaugas Cup. Moreover, Žalgiris Kaunas finished fifth in the
2025–26 EuroLeague regular season, while Masiulis was a runner-up for the 2026
EuroLeague Coach of the Year award. In the 2025–26 EuroLeague playoffs Masiulis' coached Žalgiris Kaunas faced off his former team Fenerbahçe Istanbul, coached by Jasikevičius. ==Career statistics==