Ragan began racing at age twelve in the Bandolero Series, winning the national championship in back-to-back years. He progressed into the Goody's Dash Series and then to the Legends Pro-Division, where he finished fourth in points. At eighteen he joined the Camping World Truck Series, Nationwide Series, and ARCA Racing Series simultaneously. In 2005 he won an ARCA race and recorded eleven top-tens across 19 starts. Competing in the Roush Racing Driver X programme in the Truck Series in 2004, he recorded one top-five and eight top-tens in nineteen events.
Ragan moved to the NASCAR Cup Series full-time in 2007 as the driver of the No. 6 Roush Fenway Racing Ford, replacing Mark Martin. He finished second in the 2007 Daytona 500 Cup Rookie of the Year standings and won the award outright in the Busch Series. His 2008 season was his most consistent with RFR, producing six top-fives and 14 top-tens for 13th in points.
On July 2, 2011, Ragan scored his first career Cup victory at the Coke Zero 400 at Daytona International Speedway, receiving a late push from teammate Matt Kenseth. Earlier that season he had won the non-points Sprint Showdown at Charlotte Motor Speedway, passing Brad Keselowski with two laps remaining. Ragan's win at Daytona was also notable because his primary sponsor UPS subsequently announced they would not return to the team, which contributed to RFR closing the No. 6 programme.
Ragan signed with Front Row Motorsports for 2012, an underfunded operation that required him to do more with less. His defining FRM moment came on May 19, 2013, in the Aaron's 499 at Talladega Superspeedway. Starting the green-white-checker restart in 10th place, he received a last-lap push from teammate David Gilliland to pass Jimmie Johnson, Matt Kenseth, and Carl Edwards for the win — the first Sprint Cup victory for Front Row Motorsports. Three consecutive engine failures in the subsequent Chase dropped him to 28th in points.
After stints with Joe Gibbs Racing (standing in for the injured Kyle Busch in 2015, where he posted a fifth at Martinsville) and Michael Waltrip Racing (before MWR closed at season's end), and then a difficult 2016 season with BK Racing, Ragan returned to FRM for 2017 and 2018. He delivered several strong plate-track performances including a sixth at Talladega in spring 2018 and very nearly won the 2017 summer Daytona race, leading with two laps to go before being passed by Ricky Stenhouse Jr.
His 2018 season was his best with FRM: finishing 25th in points with multiple top-25 strings, his strongest showing since leaving RFR.
Ragan ran a sixth full-time season with FRM in 2019 and announced his retirement from full-time competition on August 14, citing a desire to focus on his family. He had qualified second on the grid at Kansas — his team's best non-plate qualifying effort — and ran in the top ten deep into the Coca-Cola 600 before fading to fifteenth.
Ragan remained active in part-time roles after retirement. In the 2020 Daytona 500, driving for Rick Ware Racing, he finished fourth — his best ever Daytona 500 result. He transitioned into a test driver role for Ford Performance, contributing to development of the Next Gen Cup car. In 2024 he drove the No. 60 for RFK Racing in the Daytona 500 as part of that team's Stage60 project. That same year, NASCAR selected Ragan as the test driver for the ABB NASCAR EV prototype at the Chicago Street Course.
He has continued to serve as a rotating contributor on Fox Sports' NASCAR Race Hub programme both during and after his active driving career.
Ragan's career demonstrates how an underfunded small team driver can still carve out major victories through smart plate-track racing and precise positioning. Both his wins came at restrictor-plate events — Daytona and Talladega — where aerodynamic drafting equalises machinery. His Talladega 2013 win carries additional historical weight as Front Row Motorsports' first-ever Cup victory, establishing a small operation as a genuine race-winning team. His post-career contributions to Ford's Next Gen development and his broadcasting work have kept him engaged with the sport beyond his driving years.