The Giants have paid an undisclosed transfer fee for the 6ft 5in prop, who spent last year with Brisbane Broncos' feeder club before returning in time for the Vikings' return to Stobart Super League.
Giants managing director Richard Thewlis said: "Anthony was identified a long time back by us as being a prodigious talent and the year in Australia confirmed that from the reports we received."
Mullally, who joined Championship club Whitehaven on loan after rejecting the offer of a new deal with the Vikings, will link up with Huddersfield in November for the start of pre-season training.
"I hear nothing but good reports of all aspects of the set-up at Huddersfield and I will be moving across to live there after this season has finished," he said.
- Brisbane Broncos