The 4-1 victory at John Smith's Stadium ends their eight-match winless streak and hands AFC Bournemouth their first loss since 23 December.
Mounie set up the first on seven minutes when he raced away from Simon Francis and passed for Alex Pritchard to net his first goal since signing in January.
The Cherries then equalised as Junior Stanislas controlled Ryan Fraser's cross and slotted past Jonas Lossl.
But Huddersfield Town quickly took the match away from the visitors, Mounie converting two crosses from Aaron Mooy either side of half-time.
Steve Cook had hit a post for AFC Bournemouth with the score at 2-1 and Mooy was taken off on a stretcher with 15 minutes to play.
Rajiv van La Parra scored a fourth in stoppage time, from a penalty won by Pritchard, as David Wagner's side moved up to 16th, four points behind 10th-placed AFC Bournemouth.