Summerfield Johnston Jr. was born in 1932 and grew up on the 4,000-acre Bendabout Farm in McDonald, Bradley County, Tennessee. His grandfather was James F. Johnston, the founder of the Coca-Cola Bottling Company, the first Coca-Cola franchisee. His Father, Summerfield Johnston Sr., worked for the family Business. He graduated from the University of Virginia, where he played polo in 1951.

Johnston is a left-handed polo player. In the 1950s, he organized polo matches on his family farm in McDonald, Tennessee. He later founded the Chattanooga Polo Club, later known as the Bendabout Polo Club. He served as the long-time President of the Gulfstream Polo Club in Lake Worth, Florida. He served as Vice President of the United States Polo Association from 1979-1989, President from 1980-1984 and as Chairman from 1984-1988, and still sits on its Board as a governor-at-large. He owns the Flying H ranch in Big Horn, Wyoming, home to the Flying H Polo Club, and the Everglades Polo Club in Wellington, Florida.

He joined the Board of Directors of the Coca-Cola Bottling Company in 1959. In 1991, he merged it with Coca-Cola Enterprises. He served as its Chairman and CEO from 1991 to 2001.

In 1982, he was awarded the Hugo Dalmar Trophy for exemplary sportsmanship. On February 17, 2001, he was inducted into the Museum of Polo and Hall of Fame. He is a proponent of the return of polo to the Olympic Games.