Mounie was shown a controversial straight red card by referee Michael Oliver in the 32nd minute for his challenge on Brighton midfielder Yves Bissouma.
“Huddersfield Town’s appeal against the red card shown to striker Steve Mounie in the game against Brighton & Hove Albion on Saturday, December 1 2018 has been unsuccessful,” the club said on their official website.
Town boss David Wagner was furious at a number of key decisions made by Oliver during Saturday’s game.
The Terriers had led through Mathias Jorgensen’s first-minute header, but Brighton hit back after Mounie’s dismissal to win 2-1 courtesy of goals from Shane Duffy and Florin Andone.
“After Town submitted the appeal on Monday, the regulatory commission informed the club that the appeal had been unsuccessful, meaning Steve will now serve a three-match suspension,” Huddersfield added.
“This rules the striker out of the upcoming Premier League games against AFC Bournemouth (A) on December, 4 Arsenal (A) on December 8 and Newcastle United (H) on December 15.”
Laurent Depoitre is set to return to the starting line-up in Mounie’s absence for Tuesday night’s Premier League game at Bournemouth.
Wagner, who has no new injury worries for the trip to the south coast, was also aggrieved by Oliver and his assistants’ refusal to award Town a first-half penalty against Brighton after Alex Pritchard appeared to have been hauled down in the box.
Another contentious decision saw Brighton substitute Leon Balogun receive a yellow card for his tackle on Erik Durm in the closing stages.
“Sometimes situations like this make you stronger and give you more desire,” Wagner said. “This wasn’t what we deserved, but it’s in the past and now it’s about the next challenge.
Before news of a decision on Mounie’s appeal was known, Wagner had earlier said: “In my opinion it was anything but a red card. Immediately I spoke with Steve he didn’t want to do anything harsh or nasty. You look at it and you can see it.
“If you look at it from different angles it looks different but we have to judge it in real time and from my view it makes absolute sense to appeal.”