The pair started their NRL journey together ten years ago at Redfern when the foundation club rejoined the league after a legal wrangle.
But unlike Merritt, who spent two seasons at Cronulla, Geddes will retire a one-club player after an injury-marred career.
The 31-year-old had five of his past six seasons ended prematurely - and has played just 124 games over 11 years.
He has featured in 11 of Souths' 13 games this year, but decided this week not to pursue a 12th season.
"I wish I could play forever but unfortunately my body won't allow that to happen," Geddes said.
"I've absolutely loved my time here at the Rabbitohs. I've seen a lot of changes over the years and the club just continues to grow stronger and stronger.
"I'm proud to say that I've played all of my first grade football at the one club, which is something that not a lot of players get to do."
Rabbitohs coach Michael Maguire was full or praise for the veteran, noting he'd become a leader among younger teammates and helped turn the club around.
"Scotty has been a real trooper for this club for over a decade now," Maguire said.
"To play the position he does, with the injury issues he's had over the years, and to keep getting himself ready to play each week shows his level of commitment and professionalism.
"He has seen the whole gamut of changes to this club over the years. From reinstatement, to the ownership changes to the culture changes we're seeing now.
"He has been part of it all and has been a real leader in creating a lot of the change that you're seeing now."