Deegan began riding dirt bikes at age seven,[1] and started competing in short course off-road racing after being gifted a Trophy Kart for her eighth birthday.

[10] She is one of four women to win a LOORRS class championship in its history alongside Corry Weller, Kali Kinsman, and Megan Mitchell.

In December 2021, she participated in the Nitro Rallycross' side-by-side (SXS) support class at Florida International Rally and Motorsports Park, where she finished fifth and fourth in two races.

[22] Deegan made her debut in the season-opening East Series race at New Smyrna Speedway on February 11,[23] where she started ninth but retired on lap 19 due to mechanical problems.

[24] On March 15, Deegan made her West Series debut at Kern County Raceway Park, finishing seventh.

"[26] On May 15, Deegan was announced as a NASCAR Next class member for the second straight year[27] as one of four drivers returning to the program from the previous season.

[49] At the East season-opening race at New Smyrna, qualifying was rained out,[50] allowing Deegan to inherit pole position after setting the fastest practice time.

[51][52] Deegan led the first six laps[53] but eventually retired from the race, finishing 16th after suffering a mechanical issue at New Smyrna for the second consecutive year.

[55] Deegan earned her second career K&N Pro Series win in the event with another last-lap pass, this time on Sunrise Ford Racing's Jagger Jones.

[71] The following weekend, she had a strong performance at Roseville in K&N West, setting the fastest time in both practice sessions,[72] winning the pole,[73] and finishing second in the race.

[74] Deegan ended the 2019 season with a fourth-place finish at ISM Raceway, clinching third in the final championship point standings.

[80] At the season-opening race at Daytona International Speedway, Deegan ran the fastest lap time in the opening practice session.

[85] By mid-September, Deegan had expressed frustration with ARCA's limited practice and lack of live pit stops due to the COVID-19 pandemic, saying it "favors the drivers who have been there forever" and makes it more difficult to attract sponsorship.

"[86] She tied her career-best ARCA finish with a second-place run at the Illinois State Fairgrounds Racetrack, the series' only dirt race of the season.

[88] On October 7, 2020, DGR-Crosley announced that Deegan would make her NASCAR Gander RV & Outdoors Truck Series debut in the team's No.

[90] On October 17, 2020, Ford Performance announced that Deegan was in line to drive full-time in the 2021 NASCAR Camping World Truck Series for DGR-Crosley, which was renamed David Gilliland Racing in January.

Due to many races not having practice and qualifying as part of COVID-19 pandemic restrictions, Deegan regarded her rookie season as a "learning experience" in growing accustomed to life in the Truck Series.

[95] She was voted the 2021 Truck Series Most Popular Driver, marking the second straight season that a rookie received the award after Zane Smith did so in 2020.

Known for her aggressive on-track moves, all three of Deegan's wins in the K&N Pro Series West came after making contact with another car,[111] while her last one saw her spin out her teammate entirely.

[64] Racer's Kelly Crandall wrote in 2019, "Deegan doesn't care what anyone on or off the track thinks, and she has repeatedly made it clear she's here to win races, will do so at any cost, and then climb out and tell you all about it.

[114] At Roseville in 2018, one week after scoring her first career victory on a bump-and-run pass, Deegan was penalized one lap late in the race for contact with Trevor Huddleston.

[115] In 2019, driving in her ARCA debut at Toledo, Deegan finished last after contact with Joe Graf Jr. and declared she was "done playing nice.

"[116] Deegan's rough driving in the K&N West race at Gateway led to an argument with series veteran Todd Souza.

Souza stated that her on-track behavior was "full-on disrespect" and was quoted as saying Deegan "drives like she's a spoiled rotten little baby.

"[70] In the 2020 season-opening ARCA race at Daytona, Deegan's aggressive bump drafting nearly spun teammate Tanner Gray into the tri-oval.

[117] Despite her spotter, Eric Holmes, encouraging her to relax the aggression, Deegan later sent Chuck Hiers into the wall coming off of turn 2, leading Autoweek's Matt Weaver to write, "Such drafting tactics are generally disapproved of at Daytona and Talladega, and that's something she will have to learn.

"[117] Later that season at Lebanon I-44 Speedway, series officials gave Deegan a warning for her rough driving after she spun out two cars within the first 70 laps of the race.

Holmes said after the race, "Some drivers just don't understand what it's like to run your own team and have to pay for their own stuff, so they just...knock people out of the way every time they have to take the lead.

[123] At the 2020 Daytona 500, Deegan expressed interest in meeting President Donald Trump, tweeting the morning of the race, "Today's goal.