Dal Santo, a restricted free agent, finally became a Kangaroo after drawn out negotiations between St Kilda, North Melbourne and the player's management.
Under free agency rules, St Kilda now has the right to match North Melbourne's offer.
But there is no expectation the Saints will do that after weeks of negotiations to decide the best way for Dal Santo to move on.
The 29-year-old has agreed to a three-year deal with the Kangaroos.
Essendon was also in the mix to secure his services after briefly meeting with the experienced Saint back in September.
It is understood the Bombers met with him again this week.
However, he also met with the Kangaroos' leadership group in recent times and made a positive impression.
The situation surrounding the 260-game midfielder's future was cloudy given the Saints were open to him staying, or moving if they were compensated fairly.
A clause in Dal Santo's contract also meant he could be moved on as a restricted free agent or through a trade.
Shortly ahead of Friday's free agency deadline it was confirmed Dal Santo would wear the blue and white next season.
Soon after the Roos welcomed the skilful left-footer to the club, they published a digitally altered an image of Dal Santo wearing a North Melbourne jumper on their website.
"We identified Nick as a player we wanted and we are thrilled to have finally landed him," the club's general manager of list and player personnel Cameron Joyce said.
"He will be a valuable addition to our team for many years to come.
"Nick is an experienced, elite midfielder who will add some more class to our list."
"Nick has been a valuable part of St Kilda for a long time and will always be remembered fondly for his contribution to the club," Watters said.
"While we are disappointed to let go of a person of Nick's calibre, he moves to a new team that presents a new opportunity to him and I would personally like to wish him well for his future."
St Kilda Head of Football Chris Pelchen reiterated the move only happened because Dal Santo and the Saints were both beneficiaries of it.
"Nick has been an important part of the St Kilda football club since his debut in 2002," Pelchen said.
"He has been a valued and respected player with the Saints and it was an extremely difficult decision to allow Nick to leave our club.
"As we have previously stated, Nick's move to North Melbourne would only occur through mutual agreement and as such, we have honoured a position that is beneficial to both him and St Kilda."
St Kilda will now wait for the AFL to release the compensation it will receive, which the Saints hope will be the pick after their second-round selection.