It is generally accepted that this costume was first adopted by George Claude Lockhart on the orders of Bertram Mills in 1928, when Lockhart worked as ringmaster for his circus at Olympia, London.

Why do ringmasters wear red?

“The ringmaster's role in the circus is to roll out the red carpet, to make sure the audience is open and receptive to the acts that are coming,” he explained. ... We're rolling out the red carpet for the youth circuses of tomorrow who are coming up today. The top hat is a symbol of that.”

Where did the circus originate?

Although circus arts are ancient and transnational in origin, the modern circus was born in England during the 1770s when Philip Astley, a cavalryman and veteran of the Seven Years War (1756-1763), brought circus elements—acrobatics, riding, and clowning—together in a ring at his riding school near Westminster Bridge ...