She took top spot in the T11 100 metres, clocking 11.96 seconds, accompanied by her guide Chris Clarke.
The 26-year-old, who is registered blind and has only limited sight in one eye due to a deteriorating condition, previously won silver medals from the London Olympics in 2012 and Beijing games in 2008.
Earlier, in the semi-final, Libby believed she had achieved a personal best of 11.91 and broke the world record in the process.
There was drama for a period when she was disqualified after it was alleged that her guide had pulled her slightly at one point but later, after a British Team appeal, her victory and place in the final was reinstated.
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