After coming up through the junior ranks of Haukar, Margrét debuted with the senior team during the 2008–2009 season.

She won the Icelandic championship in after Haukar beat KR 3-2 in the Úrvalsdeild finals.

During her last season with Haukar, Margrét averaged 11.8 points, 4.5 rebounds and 3.3 assists per game.

[9] Margrét's parents, Hálfdán Markússon and Sóley Indriðadóttir, both played basketball for Haukar.

Her sister, Sylvía Rún Hálfdánardóttir, plays for the Icelandic national team.