The Austrian produced a superb performance aboard Fine Feeling to take the title with a final score of 79.150 per cent.
He finished ahead of Finland's Katja Karjalainen, who took the silver medal with a score of 74.250, while Great Britain's Lee Pearson took bronze.
The latter result represented something of a disappointment for the home crowd, who had been hoping to see Pearson claim an 11th Paralympic Games gold medal.
The 38-year-old had never been beaten in three successive Paralympics before London, but his score of 74.200 per cent aboard Gentleman was not enough.
There was, however, better news for the Host Nation in the Grade II class, where Natasha Baker won her second gold medal of these Paralympic Games.
The 22-year-old took the title on Cabral with a Paralympic record score of 82.800 per cent.
Her victory came just 48 hours after she was crowned Individual Championship Test - Grade II champion, also achieved with a Paralympic record.
Baker faced tough competition from the likes of reigning Freestyle Paralympic champion Lauren Barwick and German rivals Britta Napel and Angelika Trabert.
But she rose to the challenge superbly, delivering a high-class musical routine that was a cut above anything else.
Napel (Aquilina 3) and Trabert (Ariva-Avanti) took silver and bronze respectively, with Ireland's Eilish Byrne fourth.
An elated Baker said: 'I am completely over the moon. It was a personal best, a Paralympic record and a gold medal. That's pretty special.
'I just wanted to come and do my best, and I did. The music suits my horse so well. It is perfect for him.'