Born in Skuodas, Lithuania, he made his debut with Mažeikiai (Lithuania) during the 2002-03 championship. He played high-school basketball at Laurinburg Normal HS. He signed for the 2003–04 season by Mažeikiai. He signed for the 2004-05 season by Šiauliai and played there until the end of the 2005–06 season. He signed for the 2006-07 season by Lietuvos Rytas. Despite being a solid player at first, his career in Lietuvos rytas quickly went downward, and he was eventually released in May 2013. In August 2013 it was announced that Jomantas signed with BC Pieno žvaigždės.