The three-time Grand Final winner has signed for Rhinos on a deal until the end of this season, less than a week after being released from his contract with Wigan Warriors.
He scored 67 tries in 155 appearances for Leeds in a six-season stint which began in 2011, but left midway through 2016 to join Penrith Panthers on loan.
The former Featherstone Rovers back signed for Castleford Tigers that autumn and joined Wigan in 2018.
Now 30, Hardaker was involved in a series of controversies during his time at Leeds and missed Tigers' 2017 Old Trafford defeat by Rhinos after testing positive for cocaine.
But Rhinos are second from bottom in Betfred Super League, with just two wins from 11 competitive games this year and have injury problems at full-back, centre and wing - all positions where Hardaker is a proven performer.
Hardaker will go into the squad for Friday’s visit of Hull KR and insisted: “My focus is on playing well this year for the boys and enjoying my rugby.”
He said: “It is a very talented squad, albeit with injuries to key players at the moment.
“After our history together, I was surprised and overwhelmed when Leeds came calling and I want to make the most of this opportunity.
“I think it is a deal that works well for everyone concerned.”
Hardaker said he has “fond memories” of his time at Leeds and returning to the club is”really special”.
He said: “I have spoken to [incoming coach] Rohan Smith so we can get a feel for each other, he is arriving the same week and it was good to understand what he is looking for.
“He explained his vision for what this year looks like for Leeds as a team and explained the journey he had been on in his coaching career.
“I am sure we are both really eager to get there and do our best for the club.”
Hardaker was dropped by Wigan before Easter after coach Matt Peet said he had dipped below standards expected at the club.
“The way I left Wigan wasn’t the way I wanted to leave the club,” Hardaker added.
“This started last year when I wanted to get a chance to come home back to Yorkshire with my family.
“I have got that opportunity thankfully with Leeds and I can’t wait to play in those Friday night games in front of a packed South Stand again.
“It is definitely a case of ‘you don’t realise what you’ve got until it's gone’ and I think I let my time at the Rhinos the first time pass me by.
“Even as an away player it is special to play at Headingley and I am really keen to get going as soon as possible now.
“In the short term I need to get to know the boys, play in as many games as I can and show what I can do for the Rhinos.”
Rhinos chief executive Gary Hetherington confirmed he has spoken to Hardaker “on a number of occasions” in the past few days and stressed: “The short-term contract works for all parties in this unique situation and I am sure Zak will be aiming to show his best form on the field now he is back in blue and amber.
“Credit must also go to [interim-coach] Jamie Jones-Buchanan who was open to welcoming his former teammate back into our environment.”