Sadler grew up in Emporia, Virginia, where he and his younger brother Elliott began racing go-karts together. He progressed through late model racing in Virginia before graduating to the national NASCAR ranks. Sadler attended the University of North Carolina and is a devoted Tar Heels sports fan. He married Angie in February 1996; they have three daughters — Cora, Halie, and Naomi. Sadler has spoken publicly about his middle daughter Halie being on the autism spectrum, and has supported autism-related charities during his career.
Sadler made his NASCAR Busch Series debut in 1992 at Orange County Speedway, starting 19th but finishing 25th after wrecking his No. 32 Oldsmobile. He ran four more Busch races that season and posted a best finish of 20th.
He moved to a full-time Busch Series schedule in 1993, driving the No. 25 Shell Oil/Virginia is for Lovers–sponsored Oldsmobile for Don Beverly. That year he earned his first series win at Orange County Speedway and was named NASCAR Busch Grand National Series Rookie of the Year, finishing tenth in points. He repeated the feat with another Orange County win and a fifth-place points finish in 1994. After several more competitive Busch seasons through the late 1990s — picking up poles at tracks including Milwaukee Mile in 1996 — Sadler was displaced from his seat when his primary sponsor, Diamond Ridge Motorsports, refocused its resources on his brother Elliott's career.
From 1999 onward, Sadler ran a primarily self-funded, limited schedule in both the Busch and Winston Cup (later Sprint Cup) Series under his own Score Motorsports banner. Highlights included a seventh-place finish at Pikes Peak International Raceway in 2000, a 23rd-place run at Talladega Superspeedway in 2004, and sporadic Busch Series appearances through the mid-2000s. In 2004, former NBA player Bryant Stith became a co-owner of Score, helping fund Sadler through 30 Busch starts with a best finish of 12th at Milwaukee.
In later years Sadler became notable for repeatedly competing at Martinsville Speedway with Virginia Lottery sponsorship; the lottery backed him as a regional spokesman for races in or near Virginia. His final notable Cup start came at the 2017 First Data 500 at Martinsville, where he started last in the No. 7 Chevrolet for Premium Motorsports and finished 34th. He announced his departure from NASCAR in November 2019.
As a team owner, Sadler has the distinction of being the last competitor to race a Pontiac in NASCAR, as the manufacturer withdrew from the sport after the 2003 season. He currently co-owns Sadler Stanley Racing with politician Bill Stanley, fielding modified cars on the SMART Modified Tour and NASCAR Whelen Modified Tour.
During the late 2000s and 2010s, Sadler transitioned to a media role, working for Speed and then Fox Sports. He served as a reporter on NASCAR RaceDay and as a pit reporter for their Camping World Truck Series broadcasts. He left the network role in November 2019.
Sadler had an unusual cross-promotion relationship with Total Nonstop Action Wrestling. In 2002, TNA sponsored his racing efforts and he appeared in a storyline feud with Ron Killings. He founded the United Wrestling Federation in 2005, a promotion that initially co-operated with TNA by bringing shows to cities such as Detroit and Philadelphia. In late 2007 Sadler joined TNA as an announcer. He also hosted an online web series called Hermie's Hotseat on TNA's YouTube channel, conducting candid interviews with wrestlers and TNA staff.
After leaving professional racing, Sadler ran as a Republican for the newly redrawn Virginia State Senate District 17 in 2023. The district covers his hometown of Emporia along with Suffolk, Isle of Wight County, Portsmouth, and several surrounding counties. Despite out-raising his opponent Emily Brewer — a member of the Virginia House of Delegates — by approximately $200,000, Sadler lost the June 20, 2023 primary. Brewer was endorsed by Virginia Governor Glenn Youngkin, Lieutenant Governor Winsome Sears, and Attorney General Jason Miyares.
Sadler and his wife own several restaurants in Emporia, Virginia, including FO SHO Bar and Grille, Victory Lane Restaurant, and a Quiznos location. He and his sister also manage the family's Sadler Brothers Oil Company, which has operated truck stops and convenience stores across multiple generations of ownership.