The 28-year-old stand-off, centre or loose forward, who was in the Saints team that won the Super League title in 2014, joined Canberra Raiders at the end of last season on a two-year deal but failed to break into their NRL team and has been released.
Turner, who played in the NRL All Stars game in Newcastle in February, had been linked with a return to his old club Salford, as well as Warrington and Wakefield but the Giants have secured his services on a three-and-a-half-year deal with immediate effect.
Huddersfield, struggling in the bottom four of the Betfred Super League, recently freed up space on their salary cap with the sale of half-back Ryan Brierley to Toronto.
Huddersfield coach Rick Stone said: "It's become pretty clear to me over here that the recruitment market is a tough place and patience is needed.
"When the opportunity to bring a proven, experienced, classy player such as Jordan here became apparent we moved very quickly indeed.
"He can tick many boxes for us within our squad and I am looking forward to working with him as soon as possible.
"He has played as a strike centre, a running type six as well as in every back-row position in his career and is a good athlete who can play at well over 100kg and be mobile with it.
"We have been looking to fill a gap ever since Ryan moved on and I am delighted that our patience has been rewarded with such a good acquisition. I have asked a few of the boys here who know Jordan pretty well having played with and against him and like me they are keen to get him here to help us as soon as we can."
The Oldham-born Turner began his career at Salford, establishing himself in the team for two years before joining Hull at the start of the 2010 season.
Turner made two appearances for England Knights in 2012 before moving to St Helens, for whom he scored 61 tries in 119 appearances, including their Old Trafford triumph over Wigan.
Turner said: "I am extremely excited to be returning home to the UK with the Huddersfield Giants.
"Last year I took an opportunity that was given to me to head out to Canberra knowing how difficult it would be for me and my partner on the other side of the world and was keen to stick it out.
"In the last few months I have had plenty of opportunities to return home but turned those chances down. With the Giants, things happened fairly quickly. They explained their vision and expressed how much they wanted me to be a part of the long-term future of their great club and it was something I could not pass up.
"They are a club I've always had massive respect for playing against them over the years."
