The Pendleton Round-Up began in September 1910 as a frontier exhibition of horsemanship and cowboy skills that dazzled 10,000 spectators with its sheer speed and colorful variety over the four-day event. Organizers managed to put the first show together in a little more than three months as a community undertaking. In the over one hundred years since its beginnings, the Pendleton Round-Up has continued each year to present saddle and bareback bronc riding, steer wrestling, calf and steer roping, horse racing, and bull-riding events that capture the daring spirit and rip-roaring cowboy lifestyle of the American frontier.

The founders of the Pendleton Round-Up were among the town’s leading young professionals and businessmen. Led by lawyer Roy Raley, they wanted to hold an entertainment that would put the town of Pendleton on the map and celebrate the community's Wild West roots. Drawing on the inspiration of Buffalo Bill's Wild West shows, the Portland Rose Festival, and community fairs that featured horsemanship and rodeo skills, the Round-Up's organizers strived for something authentic and long-lasting in its presentations.

The Round-Up's performers were not mere actors recreating the past, but actual working cowboys and ranch hands who still broke wild horses and roped and branded cattle on ranches throughout the Northwest. The founders sought out the best livestock to ensure that the cowboys gave exciting, high-quality performances. Over time, the Round-Up has maintained its reputation for drawing top contestants and the highest quality livestock to put on a fast-paced, high-level demonstration of rodeo skills.

From the beginning, a key feature of the Round-Up, and crucial to its continuing success, was the inclusion of Native Americans. Round-Up promoters invited people from the nearby Umatilla Indian Reservation for the Cayuse, Umatilla, and Walla Walla tribes (now the Confederated Tribes of the Umatilla Indian Reservation) and tribal members from throughout the Northwest to participate in the event. They set up a teepee encampment next to the arena grounds and gave demonstrations of traditional dancing, horsemanship, and skills in beadwork, leatherwork, weaving, and basket making.

The overwhelming success of the first show prompted its backers to purchase land along the Umatilla River in Pendleton. They raised funds to build a wooden stadium that sat 10,000 spectators and supporting facilities, including an arena, racetrack, and corrals and barns for the livestock. Eventually, a covered, steel-and-concrete stadium that could accommodate 20,000 viewers replaced the original stands, and supporting facilities have been expanded.

From the beginning, the Round-Up staged the Westward Ho! Parade on the Friday of the four-day event. The parade, which continues to showcase fine horses, cowboy and Native American regalia, and historical horse-drawn vehicles, is reputed to be the largest nonmotorized parade in the United States.

Until 1929, tough-as-nails cowgirls competed in horse racing, bronc busting, and trick roping events. The accidental death of bronc rider Bonnie McCarroll led to the banning of women contestants at the Round-Up for over seventy years. Women contestants returned to the Round-Up in 2000 in the barrel-racing event.

In 1913, the Round-Up added a night show to the program. Roy Raley and Anna C. Minthorn Wannassay, a Cayuse tribal member, wrote a script for an outdoor pageant that depicted traditional Native American life before white settlement, the arrival of white pioneers, and the development of the West. Using pantomime, musical score, and live animals on stage, the Happy Canyon Pageant was a success from the start. The show has continued as an integral feature of the annual Round-Up. Over time, the roles of both Native Americans and whites became the virtual property of the performers and were handed down within families.

Each September, as many as 50,000 spectators crowd into Pendleton to watch the four-day, community-owned and staged event. Operated from the beginning as a nonprofit, all funds that are not used by the Round-Up Association to produce and maintain the show are donated to various local civic organizations and causes. The Pendleton Round-Up was performed during the tough economic times of the Depression, overcame a disastrous stadium fire in August 1940, and came back after a two-year suspension during World War II to thrive as one of the top rodeos in the world.