Winterbottom began motorsport on motorbikes in club-level events before moving to karting, where he became prolific. He won ten Australian Kart Championships, 25 state Kart Championships across multiple classes, and in 2001 was crowned Australian Formula A Kart Champion. He also won a Knoxville State Championship in the United States during a family holiday in 1998, and competed at the Suzuka Champions Kart race in Japan in 1999.
He transitioned to Formula Ford in 2001, finishing second in the 2002 Australian Formula Ford Championship to future rival Jamie Whincup. His karting and Formula Ford form earned him the Mike Kable Young Gun Award and a place in Stone Brothers Racing's development program.
In 2003, Winterbottom dominated the Konica V8 Supercar Series developmental championship, winning five rounds and six pole positions in what was an almost complete debut season. He joined the main Supercars field with Larkham Motor Sport for 2004 and 2005 before earning a full factory drive.
Winterbottom joined Ford Performance Racing as the driver of the No. 5 Ford Credit Falcon for 2006. In his very first season with the team he claimed a round victory co-driving with Jason Bright at the Betta Electrical 500, added further podiums, and finished a remarkable third in the championship in only his third year of main-series racing.
His 2007 season brought a solo round win in Bahrain and four pole positions — enough to claim the V8 Supercars Pole Award — though he went off while leading the Bathurst 1000. He finished second in the 2008 championship behind Whincup, with wins including a dominant clean-sweep of all three races at the BigPond 400 at Barbagallo Raceway.
Consistent podiums and round wins followed across 2009 to 2011 as Winterbottom established himself as a title contender, though he found the championship out of reach while Triple Eight Race Engineering's cars dominated.
In 2013, Winterbottom won the Bathurst 1000 alongside former teammate Steven Richards on 13 October. Despite the Mount Panorama triumph, an inconsistent start to that season left him fourth in the championship. In 2014 he led the title race by 161 points midway through the year, but the Triple Eight machines ultimately prevailed and he finished third.
The 2015 season brought Winterbottom his greatest success. Racing under the renamed Prodrive Racing Australia banner with the newly introduced Ford FG X Falcon, he won eight championship races in the mid-year stretch, including a clean-sweep of the Townsville 400, and secured his ninth win of the season at the Sandown 500 with co-driver Steve Owen. He carried the points lead through the final round in Sydney and clinched his only Supercars championship title, ending Ford's five-year drought.
He defended the title in 2016 but fell to sixth in the standings. Two winless seasons in 2017 and 2018 followed, and after 13 seasons and 412 race starts with the team — renamed Tickford Racing for his final campaign — Winterbottom departed at the end of 2018 with a record of 38 wins, 35 poles and 117 podiums.
He joined Team 18 from 2019, competing in a Holden for the first time in his career. He retired from full-time driving at the end of 2024, remaining with Tickford Racing as an endurance co-driver alongside Cameron Waters.
Winterbottom made several appearances in the Stock Car Brasil championship in 2014 and 2015 alongside the main Supercars season, recording a second-place finish at the Autódromo Internacional Ayrton Senna in 2015 with co-driver Marcos Gomes — himself a Brazilian champion that same year. He returned to Brazil in 2018, starting from the back and finishing eleventh.