Despite having most of his season ruined by a persistent hamstring injury, Chapman passed a medical test at Essendon this week and despite some interest shown in the triple premiership Cat by Carlton, Chapman has chosen to join the Bombers.
The move will see him link up again with former Geelong mentor Mark Thompson who will serve as the Dons' interim coach in 2014 in place of suspended James Hird.
The 31-year-old has reportedly agreed to a two-year deal with the Bombers and despite his injury concerns in 2013 - he only managed eight games this year - Essendon would have seen enough in his late-season form, especially his best-on-ground effort in the Cats' semi-final win over Port Adelaide, to be convinced that he still has much to offer at the highest level.
Chapman is one Geelong's greatest ever players and a cornerstone of the Cats' recent period of domination.
The strong midfielder-forward played 251 games and booted 336 goals for Geelong since debuting for them in 2000, and on top of his three premiership medallions, Chapman also has a Norm Smith Medal, club best-and-fairest and two All-Australian guernseys to his credit.
With the Bombers almost certainly set to lose impressive forward Stewart Crameri to the Western Bulldogs this trade period, Essendon will be hoping Chapman can make up for that loss as they ramp up their tilt for a premiership in the next few seasons.
Meanwhile, the Kangaroos significantly bolstered their midfield after securing the services of Dal Santo as an unrestricted free agent.
Dal Santo triggered a clause in his last contract with the Saints that would have automatically allowed him to re-sign with St Kilda for another season, but both parties agreed not to act on it.
That meant the Kangaroos were free to snap up the silky on-baller, who turns 30 in February, on a three-year deal.
Essendon were keen on securing Dal Santo's services, but the 260-gamer ultimately resisted those overtures.
St Kilda coach Scott Watters and head of football Chris Pelchen paid tribute to their departing superstar.
"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."
Pelchen added: "Nick has been an important part of the St Kilda Football Club since his debut in 2002.
"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."
The move continues St Kilda's aggressive list management strategy which has already seen them part ways with number one ruckman Ben McEvoy and just a year after another superstar Brendon Goddard joined Essendon as a free agent.
Dal Santo has been one of the Saints' best players of the past decade with three All-Australian nods to his name as well as being a runner-up in the 2011 Brownlow Medal.
The Bendigo product has also proven to be a very durable player, having not played fewer than 22 games in the past 10 years.
Elsewhere, Shane Mumford's move to Greater Western Sydney was made official on Friday with GWS trading their third-round pick (currently 35) to the Swans.