Margaret Lindsley Warden organized the first event in the United States in June 1952 at Percy Warner Park in Nashville, Tennessee. The event was called 'The Southeast's Initial One Day Event." With the help of then Major Jonathan R. Burton, now General Burton, Warden and the General wrote all of the rules, built all of the jumps, laid out the venue, and essentially did everything that now takes a cadre of organizers, professionals, and volunteers to achieve. Prior to her efforts, eventing only existed in the U.S. in the military at Ft. Riley, Kansas. Due to her intense interest and knowledge of horses, Warden believed that this format, based on the international Olympic model, and only open to the military, could be developed for the civilian horse enthusiast. Due to the success of this first event, the Three-Day Trials for the Olympics were held in Nashville the following year. Now known as the as The Middle Tennessee Pony Club Event, this event is the longest and oldest continuously running event in the United States.

Warden also founded the Middle Tennessee Pony Club in 1953 and served as the D.C. and Regional Supervisor for many years. She was a member of the Board of Directors of the U.S. Equestrian Team and was awarded the Wofford Cup in 1986 and The Founders Award from the United States Pony Club in 1989. Warden wrote the "Horse Sense" column for the Nashville Tennessean newspaper, and due to her writings and promotion of horsemanship and education, she was one of the earliest voices for the ethical and humane treatment of horses. She was a founding member of the Nashville Opera Guild and the local historical society. Through her years of reading and collecting horse-related books, she willed her library to Middle Tennessee State University. This collection is one of the largest single collections of books and papers on horse-related topics in the country.