During the 2012–13 season with Neptūnas Klaipėda, Gailius averaged a career high of 17.0 points, 5.6 rebounds and 2.1 assists per game in the Lithuanian League.

In August 2017, he signed a one-year deal with San Pablo Burgos of the Liga ACB.

[4] Gailius spent the 2019–20 season with Neptūnas, averaging 16.6 points and 2.9 assists per game.

[6] Gailius played for Lithuania national team at the 2007 FIBA U-19 World Championship, finishing in 9th place.

In 2014 coach Jonas Kazlauskas included Gailius in the preliminary 24-player list for the main Lithuania national basketball team.