He has been a member of the Althing (Icelandic parliament) since 1983 and was the founding chairman of the Left-Green Movement (Vinstri hreyfingin – grænt framboð) from 1999 until 2013.

Steingrímur was born in Gunnarsstaðir, a large sheep farm between Garður and Þórshöfn in the Þistilfjörður region of northeast Iceland (Svalbarðshreppur municipality).

In his younger days he was an avid sportsman, both track and field and also a volleyball player.

He believes that civilian institutions such as the police and the coast guard should be organized in order to provide the needed protection in the unlikely event of a major disturbance.

[3] In November 2006, he published the book Við öll – Íslenskt velferðarsamfélag á tímamótum ("All of Us – Icelandic Welfare Society at Crossroads"), laying out his political ideology.