"We announce every year how hungry we are to win, but with the progression of this team I’m heading into this new season feeling revamped and more determined than ever to get back to the top," the 38-time race winner said.
"This is one of the best-looking IRWIN liveries I’ve seen.
"It’s a bolder look with more blue across the front of the car and the addition of the iconic Bunnings green across the rear flanks, it’ll be one of the toughest cars out on track and will stand out on the grid."
Team owner Charlie Schwerkolt added: "We are so proud to race the iconic colours of IRWIN Tools for the third year of our partnership and we feel this is our best livery turnout yet for the number 18 car.
"Every year we step up our level of presentation and professionalism, and to welcome new support from Bunnings Trade, Century Batteries, and Taubmans Paint alongside our suite of premium corporate support is a real vote of confidence in what we’re building here."
Winterbottom will take to Winton Motor Raceway on Friday 19 February for official pre-season testing.
The 2021 Repco Supercars Championship will commence at the Repco Mt Panorama 500 across February 26-28. Tickets are on sale now.