The 22-year-old has also now earned a coveted double-double following her triumph in the B&VI sprint on Friday.
Australia's Jessica Gallagher was up first at the Anna Meares Velodrome and threw down the gauntlet with an impressive time of 1:07.165, beating the Games record set by Thornhill when she triumphed in Glasgow four years ago.
Aileen McGlynn of Scotland was next to race and while she too posted a respectable time - 1:08.993 - she was ultimately destined for the bronze medal.
Over to Thornhill, then, who came out of the traps at full speed, completing the second quarter of the race in just 14.144 seconds before finishing in a time of 1:04.623.
That was not only enough to secure gold and a new Games record but also better the world record of 1:05.079 she had set at the Paralympics in Rio de Janeiro some 18 months earlier.