Although McGuire's running career was short, she won six AAU titles, in three different events. Her specialty, however, was the 200 m/220 y, in which she won four of her six national titles. In 1964, she was undeafeted in her favourite event, and went to Tokyo as the main contender for the 200 m gold medal at the 1964 Summer Olympics.
McGuire first competed in the 100 m in Japan, and lost out in the final to team mate Tyus. But in the 200 m final, she held off Poland's Irena Kirszenstein to take the gold medal. She added a third medal to her tally as a member of the American 4 x 100 m relay team, which placed second to Poland.