The Championship club announced yesterday that they had made the final decision to sack their manager after Friday night’s 2-1 defeat at home to Fulham.
The 36-year-old German manager had been in charge for seven months in Huddersfield, losing 15 of his 19 matches at the helm and winning just one.
Huddersfield were part of the bottom three who were relegated from the Premier League last season, with Siewert failing to maneuver an upturn in fortunes after replacing David Wagner in January.
Their poor form has continued this season, with the Terriers winless from their opening three Championship games.
They have also been ruled out of the Carabao Cup by Lincoln.
A club statement read: “Huddersfield Town has this evening terminated the contract of head coach Jan Siewert with immediate effect.” A sad news.