He held his first government post in the Ministry for the Interior and Public Order as a Deputy Minister, from 25 July 1985 until 25 April 1986.

From 9 September 1988 until 18 November 1988, he held the post of Deputy Minister of National Education and Religious Affairs.

On 15 September 1995 he was appointed as Minister for the Interior, Public Administration and Decentralisation, a post which he held until 22 January 1996.

Haris Kastanidis was expelled from the PASOK parliamentary group after voting against Greece's loan deal with its foreign creditors.

On 14 March 2012 he and Louka Katseli formed the Social Agreement party, which failed to win a seat at the May 2012 election.