Bradley was born in Hinton in Caddo County in western Oklahoma to Ralph Thomas Ottinger (1904–1970), who was employed in road construction, and the former Zulema Young (1903–1987), a teacher. Bradley had three siblings: Helen, born March 20, 1930, Ted Calvin, born August 27, 1938, and Linda Sue born November 24, 1943. Bradley later lived on a wheat farm near Hydro on the line between Caddo and Blaine counties. Even as a nine-year-old, Bradley participated in the 4-H Club, having shown lambs and pigs. At the time, girls were not permitted in Future Farmers of America, but, spurred by her uncle, Ted Ottinger, she became focused with a career in livestock and ranching, She graduated with distinction from Hydro High School, where she was a member of the state championship girls’ basketball team in 1948.
From 1949-1953, Bradley attended Oklahoma State University in Stillwater, where she was the first female student to major in animal husbandry and where she met her future husband, Billy Jack Bradley (also born 1931). The couple married in 1955 and had two children, Monte Jack Bradley (1958–1984), who died in an automobile accident, and Mary Lou Bradley-Henderson, an accountant by profession who came to work with her mother at the ranch on her brother’s death. Billy Jack Bradley left the ranch in the middle 1990s for personal reasons and resides in Vernon, the seat of Wilbarger County west of Fort Worth.
The Bradley 3 Ranch began in 1955 during a time of drought with 3,000 acres (12 km2) purchased by Minnie and Billy Bradley, and his parents, Raymond Jack “Rusty” Bradley and the former Lois Chaney, originally from Electra in Wichita County, Texas. The family maintains that Rusty Bradley’s father, Rufus Jack Bradley, had in the 1870s been a wagon boss on the famed XIT Ranch west of Amarillo, although that ranch did not actually exist until 1885. The Bradley 3 (originally three ranches) began raising Angus cattle some two years after its founding. The ranch uses Angus bulls to increase the production of the Hereford heifers.
In the center of the ranch is a slightly elevated area on which one can see the lights of Childress, the seat of Childress County, eleven miles (18 km) to the south and Memphis, the seat of Hall County, some nineteen miles (31 km) to the west. On that same spot during the day, one sees only endless ranchland covered in short grass, mesquite, juniper, and the black Angus. Not even a water tower dots the horizon from the Bradley 3. The Panhandle has been described as one place on earth where one can see the fartherest and still see the least.
Bradley’s herd usually numbers about four hundred to five hundred heifers and two hundred bulls. The ranch is owned by Bradley and her daughter, Mary Lou, and Mary Lou’s husband, James Henderson. Mary Lou is hence the fourth generation of Bradleys to ranch in north Texas. The Bradley 3 supplies seedstock to commercial ranchers in the Southwest. There are only two full-time workers for the ranch, Phil and Bob. The cows require human assistance at birth, a process known as “pulling calves” from the womb. At 2 a.m. during calving season, Bradley boards her pickup truck and drives past the pens, and with her searchlight looks for pregnant cows in distress and, as needed, summons for help. She cooks all three meals for the ranch, sometimes serving a half-dozen persons. For each meal, she uses beef from her own feed yard and packing facility. In 1986, the Bradleys developed B3R Country Meats in Childress. They were instrumental in defining national standards for natural beef products. In 2002, the company was sold to George Gillette. Bradley, supplied the steaks for the January 20, 2001, presidential inauguration of George W. Bush.
In addition to her breakthrough work at Oklahoma State, Minnie Bradley was in 1952 the first woman to win the International Livestock Judging contest held in Chicago. She was one of the first women to serve on the board of directors of the trade association, the American Angus Association, the largest beef organization in the world with 36,000 mostly male members in all 50 states. She became its first and thus far only female president in 2004. Nevertheless, Bradley rejects the role of "pioneer for women". She has no plans to retire so long as her health permits her to continue operating the ranch.
In 2006, Bradley was inducted into the National Cowgirl Museum and Hall of Fame, having joined the ranks of some 180 other trailblazers, including Dale Evans Rogers, Patsy Montana, Patsy Cline, Sandra Day O'Connor, and Georgie Sicking. Bradley was honored principally for her role in encouraging women to enter the fields of livestock breeding and management. On receiving her award, Bradley retorted that she was unaccustomed to being in a room with so many women, for most of her life had been spent in the company of men on the ranch.
She teaches students in the ranch management program at Texas Christian University in Fort Worth. Andrew M. Bivins, part of the management team of his family’s historic JA Ranch near Amarillo graduated from that same program. Bradley also hosts students from other universities.
To maximize the output from their holdings, the Bradleys lease their lands during hunting season. Minnie Lou has issued ten suggestions to her temporary tenants. One is “No litter”; anyone caught littering, and that includes cigarette butts, will not be invited back to hunt on Bradley 3 land. She insists that guests treat her as a friend, not as a business associate, and that they stay in communication: “We have a busy ranch, so I like to have hunters call ahead of time and let me know when they’ll be there. All of my hunters are great at communicating when they plan on being out and are always quick to let me know if they see any problems on the ranch.”
Bradley said that the ranch leaves no time for hobbies. “I’m always trying to improve the ranch. It’s not the biggest, but I want it to be one of the best. It’s only 11,500 acres, but there’s a lot of work to do – controlling brush, improving the grass. We’ve gone from 250 cows to about 400 cows and that takes some work. We’re in the heart of the Texas deer and quail country, too, so we lease out some land to hunters.
Bradley has received numerous awards, including the Texas Parks and Wildlife Land Stewardship Award, which was presented to her in 1998 by then Governor George W. Bush. In 2004, the Bradley 3 was listed among the top forty beef producers in the nation by ‘’Beef’’ magazine.
The Bradley 3 also won the Outstanding Rangeland Stewardship Award presented jointly by the Texas division of the Society for Range Management and the Texas and Southwestern Cattle Raisers Association in Fort Worth. The award recognizes a TSCRA member with outstanding land management activities. Bradley protects the forage that feeds her beef and the brush that sustains the wildlife population.
Bradley accepted the award at an awards chuckwagon luncheon held at the Muleshoe National Wildlife Refuge south of Muleshoe, the seat of Bailey County near the New Mexico boundary. “My lifetime goal has always been to leave the ranch in better condition than when I came here,” she said.
Bradley is included in the "Listing of Great Texas Women" sponsored by the University of Texas. She has been featured in various ranch magazines. She was the focus as “trail boss” in a February 23, 2008, segment of Bob Phillips’s Texas Country Reporter syndicated television series.
Bradley contends that the Angus have been good to her. In an interview with screenwriter Anne Rapp, Bradley acknowledged that "Most women don’t want to live out this far. You either love it, or you hate it. I love this old country. It’s the best friend I’ve had for fifty years, and it’s never let me down. It’s taken care of me, this old country. So I take care of it.”.
Bradley is Methodist. On July 22, 2008, she underwent successful heart by-pass surgery in Amarillo.
On March 18, 2011, Bradley addressed a symposium, "The Heritage of Ranch Women in Coleman County", sponsored by the Circle C Cattlewomen of Coleman in Coleman County. The event was held in the Coleman Library.