Sunday's race in Newcastle will be the elder Kelly brother's 541st race in the championship, with 19 race wins to his name for teams the like of HRT, the KMart Racing Team and Perkins Engineering, while the most recent of his 28 podiums have come with Nissan Motorsport, the race team he co-owns with brother Rick.
Kelly conceded a persistent injury was part of the reason behind his decision to step away.
"I've decided to hang up the helmet at the end of this season," Kelly said.
"To have a 20-year career doing something you love is pretty special. It's been a long, solid and clean career of being a professional driver. And even though I would probably change a few things if I had my time again, there's not anything I regret over that period.
"I love driving, and that's what kept me going for 20 years. I love getting the most out of a car. I love going around a fast corner having the thing sideways at 240km/h. The fear factor has not crept in as I've got older, so I've not lost any of that enjoyment at all.
"I've had knee surgery twice this year, and it's been a decent battle.
"Although, there have been positives for having a dodgy knee. I had gone 20 years without perfecting left foot braking, and at SMP this year I had to left foot brake all weekend.
"By the end of the weekend, I'd gotten pretty good at it. But in such a competitive sport that's not something you want to develop during an event."
Kelly began his career racing go-karts before progressing to Formula Ford, contemporaries with Garth Tander, Marcos Ambrose and Jason Bargwanna, all drivers that would become rivals in Supercars in the years to come.
He and Bargwanna were among the first group of drivers selected for the Holden Young Lions program in 1997, and although Kelly wouldn't get the nod for a race seat that year - and would make his Supercars race debut at the 1998 Bathurst 1000 with renowned privateer John Faulkner - he would make his full-time championship debut with HYL in 1999.
Kelly's maiden race win would come on the streets of Canberra in 2000, before graduating from the HYL program into Tom Walkinshaw Racing's newly-formed KMart-backed sister squad to the all-dominant HRT in 2001.
A further promotion would come in 2003, Kelly joining Skaife at the Holden Racing Team, where he would have his best years in the sport. 14 of his wins would come with the General's lead squad, including his Bathurst win and the team's 50th round win at Supercars' sole event at Shanghai in China in 2005 on his way to a career-best fourth in the championship.
Moving to Perkins Engineering in 2008, he would net the legendary team's final race win at Symmons Plains before it was taken over by he and his brother Rick at season's end. Kelly's two most recent podiums came in 2011 at Hamilton and Sandown, the brothers sharing the dais at both Hamilton and Sandown that year with Rick in first place and Todd in third.
The team's switch to Nissan at the dawn of the Car of the Future era in 2013 saw the elder Kelly's form dip but there have been flashes of speed in recent seasons, albeit often cruelled by bad luck or unreliability as the Japanese marque endured a rough period of development against the sport's traditional heavyweights.
As co-owner, Kelly will naturally remain involved with the team beyond the end of his days as one of its drivers.
"Going to an event and not jumping in the car will take a lot of getting used to," he said. "I mean, I don't even know where to stand in the garage!
"We've spent a great deal of time getting good people into roles within the team, and I've spent my whole driving life in a car on the other end of the headset. So I don't see myself putting the headsets on now taking over other people's roles in the team.
"But I certainly have a keen eye for detail, whether it be from car prep to the engineering of the cars. That would be an area I'd like to put a lot of focus in, especially with the driver line up we'll have next year.
"With Simona completing 12 months and progressing extremely well, this would allow me to put a bit more time to oversee how she is going."
Nissan Motorsport has yet to announce who will take over Kelly's seat in the No. 7 Altima next year.