Þráinn Bertelsson (born 30 November 1944) is an Icelandic film director, writer, politician, journalist and newspaper editor. He moved into politics in the wake of the financial crisis in 2008, and was elected a member of the Althing in 2009, initially for the Citizens' Movement. He later left the party to become an independent MP, before joining the Left-Green Movement, which he currently represents.

Þráinn has written, directed and produced seven feature films. His 1981 film Jón Oddur & Jón Bjarni (English title: The Twins) won a Silver Award at the 1982 Giffoni Film Festival. His 1989 film Magnús was nominated for two European Film Awards, for best picture and best script, and received the 1990 DV Cultural Prize in Iceland. He was the first filmmaker to be granted a lifetime award by the Althing. He was a co-founder of Norðan 8 and in 1982 founded his own film company, Nýtt líf (New Life Ltd.). He served a year as chairman of The Association of Icelandic Film Directors.