Former Adelaide champion Goodwin, who led Melbourne to the drought-breaking 2021 flag, has been let go by the Demons following just seven wins this season.
Taking over from Paul Roos in a succession plan for the 2017 season, Goodwin led Melbourne to their first premiership in 57 years.
But with just three games to go this season, Melbourne have made the call to part ways with the 48-year-old.
The decision is effective immediately, with former Port Adelaide and Richmond defender Chaplin to start coaching against the Western Bulldogs this Sunday.
Melbourne officially confirmed Goodwin's departure, three hours after news first broke on Tuesday.
Goodwin will front a press conference, alongside president Brad Green, at the MCG on Tuesday at 1pm.
"Goody should be incredibly proud of what he's achieved at the Melbourne Football Club," Green said in a statement.
"To take a group of players and help shape them into a premiership team is something only four other AFL coaches have achieved within the history of the club.
"He has given absolutely everything, not just as a coach, but as a person and we are extremely grateful for his contribution to the red and blue.
"While decisions like this are never easy, the Board and I believe that now is the right time for a new voice to lead our AFL playing group and program forward."
The vacancy at Melbourne could hold appeal for premiership coaches Adam Simpson and John Longmire, who have spent this year working in the media after their respective exits from West Coast and Sydney.
Long-time Port Adelaide coach Ken Hinkley is also three games away from handing his job over to Josh Carr, and it is understood he would be open to another senior position.
After giving up a record 46-point three-quarter-time lead to lose against St Kilda, the Demons responded last Saturday with an 83-point demolition of lowly West Coast.
But off-field turmoil and dwindling performances on the field since the 2021 premiership increasingly placed Goodwin's job in jeopardy.
Until four years ago, the legendary Norm Smith had been Melbourne's most recent premiership coach back in 1964.
Goodwin remained defiant until the end, saying he wouldn't be "consumed by the noise" that followed the round-20 capitulation against the Saints.
"I feel incredibly supported by the board, I have for nine years," Goodwin said last Thursday.
"We've been able to go through these challenges before with clarity and strength and stability to create success."
One of the youngest premiership teams of the modern era, Melbourne began their flag defence in 2022 by winning their first 10 games of the season.
But after their stunning second-half grand final demolition of the Western Bulldogs four years ago, the Demons suffered straight-sets finals exits in 2022 and 2023.
Melbourne finished 14th last year, and are 12th with three weeks to go this season.
Two of the stars of the premiership season, Christian Petracca and Clayton Oliver, have suffered significant and differing off-field challenges and have failed to get back to their best form.
Oliver almost left the Demons during the 2023 and 2024 trade periods, while Petracca was disgruntled at the end of last season and would have left the club had a suitor been able to organise a deal to secure him.
Long-time chief executive Gary Pert stepped away from the Demons at the end of last year, and president Kate Roffey also exited her post after bungling the situation around Petracca and Oliver.
Former Demons champion Green is the current club president, holding the post until successor Steven Smith returns from an extended overseas stay.
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