[2] In 1964, she competed in four events in the Tokyo Olympic Games, finishing fourth in the 400 metre medley.

Although she had represented her country as an Olympic swimmer the year before, she specialized in fairly short distances and had never swum more than one kilometer at a time before—the Channel, by contrast, is 35 km.

The swim, in a counterclockwise direction, was sponsored by Cathay Pacific and began and ended in Repulse Bay.

McGill faced difficulties including jellyfish stings, pollution, raw sewage and dead pigs in the water, ships, and inclement weather.

McGill's record was beaten on 11 November 2017 by Simon Holliday, who swam the distance in 12 hours, 32 minutes.