After 26 games with the Kangaroos, Delaney requested a trade at the end of the season, having fallen behind the club's key defenders Scott Thompson and Nathan Grima.
In 2013, Delaney played only the final five games of the year. North Melbourne offered him a new contract but he made the decision to leave in search of more opportunities at senior level.
The Saints made no secret of their desire to find some key defenders and Delaney looks primed to slot into a key defensive role for the undersized backline.
Delaney's manager, Greg Size, said it was a tough decision for his client to leave North Melbourne, but felt he could really contribute at St Kilda.
"The meeting we had with Chris Pelchen, Scott Watters and Ameet Bains really excited Luke. They were very clear on where they were headed and they made no bones about [the fact] there was probably going to be some tough times before the good times," Size said.
"Luke could see he had an opportunity to play regularly and also have some input and perhaps guidance to the younger players."
Delaney made his debut in round nine, 2011 after being a selection in the 2010 rookie draft.
He looked good in 2012, playing 13 games and performing well on power forwards such as Jonathan Brown and Tom Hawkins. However he was not selected for the Kangaroos' final against the Eagles that year.
Delaney struggled to break into the team in 2013 despite consistent form in the VFL.
"It’s disappointing to lose Luke, but he expressed a desire to seek opportunities elsewhere," North list manager Cameron Joyce said.
"We had offered him a new contract, but he opted to move clubs and we wish him well for the future."
Delaney told North's website that leaving the Kangaroos was a tough decision.
"I didn’t want to leave North and the hardest thing will be to leave all my friends and everyone at the club. North gave me the opportunity to play AFL and ideally, I would have loved to have stayed," he said.
"At the age I’m at, I just needed to consider my options and find a club that would be able to provide more opportunity."
North Melbourne gained St Kilda midfielder Nick Dal Santo on Friday and the two clubs swiftly negotiated a trade for Delaney shortly after.
