Cunningham, 40, left his role with Saints in April and will work alongside head coach Neil Jukes at Leigh.
Owner Derek Beaumont has relinquished the head of rugby position because of his business commitments.
Leigh have won one and lost one of their two fixtures in the Qualifiers, after finishing 11th in Super League.
The Centurions have five games left this term to secure their Super League status for next season.
Beaumont said: "Keiron has substantially more experience than myself and I feel his appointment will bring in someone with a fresh pair of eyes and a different approach, as well as a different voice around the place to freshen things up.
"I still have the utmost confidence in Neil Jukes and my coaching team and their ability to achieve our goals, which I believe will be increased by Keiron's presence."
Cunningham, a former St Helens, Wales and Great Britain hooker, added: "I have not come in to take anyone's place, but to add my knowledge and experience at this stage of the season. I get on well with Neil and he is a good friend.
"Derek has brought me in to ease the burden on Neil and bring my experience to Leigh. Hopefully I will bring a new set of eyes and structures and I'm delighted to have been given this opportunity."

He said Manila would not "break or abrogate existing treaties", suggesting he wants to maintain the Philippines' ties with the US.
It comes days after Manila announced it was suspending annual joint military exercises with the US.
Relations between the old allies have become strained in recent months.
Washington has voiced concerns over the newly-elected president's "war on drugs", which has left more than 3,500 people dead in a matter of months. Mr Duterte has called President Barack Obama a "son of a whore".
Mr Duterte, who is visiting Beijing next week, has previously suggested China and Russia could be possibly alternate partners.
But while Mr Duterte reiterated in his latest speech that the traditional joint exercises with US troops would be stopped, he said he would not break the mutual-defence treaty entirely.
``I insist that we realign, that there will be no more exercises next year," he said.
He added: "We need not really break or abrogate our existing treaties because they say that it could provide us with the umbrella.
"We will maintain all military alliances because they say we need it for our defence." He did not explain who he meant by "they".

The 35-year-old threw a new F51 European record of 17.68m to score 1100 points and finish ahead of team-mates Josie Pearson and Gemma Prescott.
It beat the previous best of 15.83 set by Ireland's Catherine O'Neill in 2001.
"I'm throwing well at the moment and once I got the big throw, I knew the pressure was off," said Butterfield.
The Glasgow-based newcomer, who was left paralysed by a tumour on her spinal cord in 2011,  took up athletics earlier this year via the talent identification programme Girls4Gold after playing wheelchair rugby for a couple of years.
"Because I was already doing rugby and the strength and conditioning work with that, I just had to try to adapt that to athletics," she told BBC Sport. "I've loved it and trained hard but I know I have a lot more to learn.
"Representing GB for the first time here has been a bit surreal but the team has been great and everyone has been really welcoming.
"The difference sport has made to me is huge but I never dreamed I would be part of this so soon."
Compatriot Pearson was frustrated after three of her six throws were deemed to be fouls.
"There was a technical issue with my throws with an official saying I was breaking some of the rules," she said.
"I've been throwing the same way all season and not been pulled up on it before so it is frustrating for this to happen at a major championship where I know I could have thrown further."
Former St Helens head coach Keiron Cunningham has been appointed head of rugby at Leigh Centurions for the rest of the 2017 season.
[NEXT_CONCEPT]
President Rodrigo Duterte says the Philippines will not end alliances with other countries, despite his increasingly anti-US rhetoric.
[NEXT_CONCEPT]
Debutant Jo Butterfield led a British clean sweep of the medals in the women's F32/51 club throw at the IPC Athletics European Championships.