Mooy, who was loaned out to Town in the Championship last season from Manchester City, will reportedly join the club on a £10m ($AU16.7 million) transfer fee.
The Australia international will become the most expensive signing in the club’s history, after he won the club’s player of the season award.
It is also reported that Mooy has agreed to personal terms of £35,000 ($AU59,000) a week.
Huddersfield’s previous record transfer fee was only £1.8 million, for German defender Christopher Schindler last year.
Mooy made 51 appearances for Huddersfield last season, scoring four goals.