They announced the signing of the centre/second-row - on a three-year contract starting in 2020 - back in May but today revealed he had joined with immediate effect.
Huddersfield recruited Wales international Butler on a loan deal from the Championship outfit before last Friday’s transfer deadline but only made it common knowledge today.
As they continue to fight against relegation - Giants are only two points from bottom in Super League with just four games to go -having the 23-year-old on board will certainly help strengthen their cause.
With Halifax out of play-off contention and Huddersfield still struggling with injuries, Woolford admitted: “It made sense to have another player available in the run in and a fresh face.
"We’ll have a look at him in training in both the centres and back-row area.
"Whilst he’ll remain part-time to fulfil the promises he’s made to his employer I’m sure we can get enough work into him if we need him to step up and make his Super League debut.
"It will be a challenge for him, but it will put some pressure on some of our guys knowing he’s there ready to have a crack"
Butler - who was due to start pre-season training with Giants in November - said “I’ve trained today and met all the lads and I’m ready to go if Simon thinks I can do a job.
"I had planned obviously to come in later in the year but there is a chance now and I’m happy to work around training and start the process of integrating into the club.”
Huddersfield host Castleford Tigers on Sunday.