Cobb began racing in 1991 at Lakeside Speedway, where her father Joe Cobb also competed in the modified division. She made nine starts in the ARCA Racing Series from 2002 onward, recording three top-ten finishes in three starts in 2004 while driving for Keith Murt. That same year she made her NASCAR debut in the Busch Series at Homestead-Miami Speedway, driving the No. 50 Chevrolet for Keith Coleman Racing. A crash on the second lap ended her race with a 43rd-place finish.
Her early Truck Series appearances came in 2008 and 2009 as a fill-in driver for various underfunded teams. In 2008 she ran the Built Ford Tough 225, starting 35th and finishing 26th; the following year she drove for Derrike Cope Inc. at the O'Reilly Auto Parts 250 before suffering engine trouble.
In 2010, Cobb purchased the assets of the No. 10 truck team from Rick Crawford's Circle Bar Racing and began competing full-time in the Truck Series under her own banner. She retained the truck number and the associated owner points, a shrewd move that gave her team instant standing in the series. That season she became the highest female points finisher in history across any of NASCAR's three major national series, achieving 17th place in the Truck Series standings.
Her best on-track result in that era came in 2011 when she finished sixth at the NextEra Energy Resources 250 at Daytona International Speedway, setting a new record for the highest finish by a female driver in the Truck Series. That record stood for nine years until Natalie Decker bettered it with a fifth-place finish at the same event in 2020. During 2011, Cobb also ran the first five races of the Nationwide Series in the No. 79 for 2nd Chance Motorsports before a dispute with the team owner led to her departure.
Also in 2011, Cobb partnered with U.S. Army Family and MWR Command to launch Driven 2 Honor, an initiative that hosted female service members and their guests at the first five Nationwide Series races of the season.
Through the middle part of the decade Cobb continued running full-time schedules in the Truck Series. Her 2014 campaign included a season-best 13th-place finish at the SFP 250, with a handful of other results in the high teens and low twenties. She also made occasional Xfinity Series starts with Rick Ware Racing during this period.
Two on-track incidents in 2015 attracted significant attention. At the Lucas Oil 200 at Eldora Speedway, Cobb was apparently spun by Tyler Reddick and confronted his truck on foot after the incident, drawing a five-thousand-dollar fine from NASCAR. Later that year, during a Truck Series event at Canadian Tire Motorsport Park, a cell phone was observed being removed from her truck during practice. Cobb was penalized under the no-cell-phone rule and fined an additional twenty-five hundred dollars for the infraction occurring while she was still on probation from the Reddick incident.
In 2018, Cobb expanded her experience internationally by joining the NASCAR Whelen Euro Series, making her series debut at Circuit Ricardo Tormo in Valencia with Racing Total.
In 2020, Cobb produced one of the defining performances of her career when she led a personal-best 16 laps at Talladega Superspeedway before ultimately finishing 24th. The following year, she was slated to make her NASCAR Cup Series debut at Talladega in the No. 15 for Rick Ware Racing, but NASCAR did not approve the entry, citing her lack of prior Cup car experience. J. J. Yeley ran in her place.
By 2022 Cobb announced she would scale her team back to a part-time schedule, citing funding and equipment limitations. The 2025 season marked the first year since her Truck Series debut in 2008 that she did not take part in the series.
Jennifer Jo Cobb's career stands as one of the most sustained female driving efforts in NASCAR history. By running her own team for the better part of a decade, she demonstrated that a woman could compete consistently in the Truck Series while also managing the considerable logistical and financial demands of ownership. Her 2011 Daytona sixth-place finish remained a benchmark for female drivers in that series for nine years, and she served as a visible advocate for women in motorsport through initiatives such as the Driven 2 Honor program.