Tómas started his senior team career with Valur during the 1981-82 season and with them won the national championship and Iceland Cup in 1983.
[8] In August 2012, he replaced Helgi Jónas Guðfinnsson as an assistant to the Icelandic men's national team.
[10] Tómas is married to Anna Björk Bjarnadóttir, a former member of the Icelandic women's national basketball team.
Together they have three children and two of them, Bergþóra Holton Tómasdóttir and Tómas Heiðar Tómasson, played basketball in the Icelandic top-tier leagues.
Tómas' uncle was Helgi Jóhannsson, one of the main pioneers of modern basketball in Iceland.