The 61-year-old had been assisting Derby County boss Paul Jewell following his arrival at Pride Park in November, but has been given permission to leave to return to full-time management.
Ternent has previously managed Blackpool, Hull City, Bury, Burnley and Gillingham during a 20-year managerial career.
"I would like to thank Stan Ternent for the hard work he has put in for Derby County and the support he has given Paul Jewell," said the County chairman Adam Pearson.
"We have given him permission to join Huddersfield Town as their manager, we have not sought any compensation."