Katherine Legge is rewriting the script in a sport where most careers are defined by youthful vigor and early appearances. On Sunday, the 44-year-old racing veteran makes her Nascar Cup Series debut at the Shriners Children’s 500 at Phoenix Raceway.

Adding to the significance of her entry, Ms. Legge will be the first woman to race in a Cup Series event since Danica Patrick ended a nine-year Nascar career at the 2018 Daytona 500.

 “I don’t want to just be a female driver for the sake of ticking a diversity box, right?” Ms. Legge said recently. “I want to be there on merit, and I want to be a good example for everybody that’s coming up behind me.”

Born at Guildford, England, Ms. Legge is a 20-year veteran of motorsports, having raced in the Indianapolis 500 four times, including 2023 when she set the record for the fastest-ever qualifying time for a woman. This is the first time she’ll compete in a Nascar event.

Ms. Legge will drive the no. 78 Chevrolet for the Live Fast Motorsports team owned by B.J. and Jessica McLeod. Ms. Legge is the 17th woman to compete in a Cup race, a list that includes Hall of Famer Janet Guthrie, who drove 33 races between 1976 and 1980.

“Entering the Nascar Cup Series is a dream come true,” Ms. Legge said. “I’m excited to team up with Live Fast Motorsports for Phoenix. …. Racing stock cars has been an incredibly fun and new challenge that’s given me a renewed sense of vigor for this sport. As always, I’m grateful for the opportunity to do what I love and am inspired by all of the effort, preparation and behind the scenes work it takes to get there.”

Live Fast Motorsports is a part-time entry in the Nascar Cup Series. B.J. McLeod drove the no. 78 to a 22nd place finish at the Ambetter Health 400 at Atlanta after failing to qualify for the Daytona 500. The car did not compete last week at the EchoPark Automotive Grand Prix at Circuit of Americas at Austin, Texas.

“We’re happy to partner with Katherine for this race,” Jessica McLeod said. “The opportunity to have such a versatile and dynamic championship-winning driver join our program is exciting for everyone on our team. This partnership reflects our commitment to providing opportunities for drivers making their way into the Nascar Cup series.”

The no. 78 hasn’t proven to be fast enough to contend at Phoenix, where Christopher Bell’s no. 20 Toyota is the favorite, having captured back-to-back wins at Atlanta and at the Circuit of the Americas. Mr. Bell, the first driver since Kevin Harvick in 2018 to win two of the season’s first three races, is also the defending winner in Phoenix.

“I’m ready to keep adding to it,” Mr. Bell said. “Winning has certainly become harder. More guys are capable of it. Whether that’s a good or a bad thing is debatable, but it’s the sport that we live in and compete in right now.”

No Cup driver has won three straight since the introduction of the Next Gen Cup car in 2022. Kyle Larson is the last driver to win three straight Cup races, which he did twice in 2021.

“I think it’s a testament to this team,” Mr. Bell said. “They have no weaknesses. We can win at any race track at any time.”

While Ms. Patrick’s Nascar debut at age 29 in 2012 received much more hype, Ms. Legge’s arrival comes with more credentials. In addition to racing in the Indy 500, Ms. Legge’s motorsports highlights include starts in the Nascar Xfinity Series, the IMSA Weather Tech SportsCar Championship, and the 24 Hours of Daytona.

Ms. Legge looks forward to the competition with the sport’s best drivers. “I have to prove competence at the end of the day, right?” she said. “I don’t think anybody expects me to go out and set the world on fire and be competitive because it’s the most competitive championship in the world. I just don’t want to make any mistakes and look silly or look incapable. I think the competitiveness will come with experience.”