Even before his succeeded his father as Elector of Saxony, in 1672 he took an active role in the administration of the Oberlausitz region. Once he did succeed on the death of his father in 1680 he took control of the government, restricted the court and created a Saxon standing army. He led his troops against the Turks and took part in the liberation of Vienna in 1683, and also fought against France.
He died at Tubingen on 12 September 1691 (old style), taking part in another campaign against France, despite various physical ailments. He was buried in the Nordkapelle in the Dom St Marien, (Collegiate Church of St Mary) at Freiberg, Saxony.
He was nicknamed the 'Saxon Mars' (Sachsen Mars) for his warlike qualities and successes, but this fails to take into account his duty to the governing of Saxony as well as an interest in courtly culture and art.
Marriage and children
He had married on 9 October 1666 (old style) at Copenhagen,Anna Sophie, Princess of Denmark, daughter of Frederick III, King of Denmark and his wife, Sophie of Brunswick-Luneburg.
They had issue 2 sons;
Johann Georg IV, born 18 October 1668 at Dresden, succeeded his father as Elector of Saxony;
Friedrich August I, born 22 May 1670 at Dresden, succeeded his brother as Elector of Saxony, and also King of Poland as August II.
Johann Georg III also had an illegitimate son;
Johann Georg Maximilian Fürstenhoff (later von Fürstenhoff), born 1686, probably at Dresden, who became an architect and engineer, and died at Dresden 15 July 1753. His mother is stated to be the opera singer Margarita Salicola in a number of Wikipedia articles (see below for links), but without citing any sources for this information. His mother is unknown or not named in both Löffler and Heckmann.
Further biographical detail
For more information about Johann Georg III see the following articles;
Heckmann, Hermann. 'Fürstenhoff, Johann Georg Maximilian von', in Sächsische Biografie, hrsg. vom Institut für Sächsische Geschichte und Volkskunde e.V., bearb. von Martina Schattkowsky, Online: http://www.isgv.de/saebi/ ( viewed 8 July 2017).
Huberty, Michel; Giraud, Alain; Magdelaine, F. & Magdelaine, B., L'Allemagne Dynastique: Les quinze Familles qui ont fait l'Empire, Tome 1 Hesse-Reuss-Saxe, France, Le Perreux : Alain Giraud, 1976.
Posse, Otto, (ed.). 1897. Die Wettiner: Genealogie des Gesammthauses Wettin Ernestinishcer und Albertinischer Linie mit Einschluss der regierenden Häuser von Grossbritannien, Belgien, Portugal und Bulgarien, Leipzig und Berlin: Giesecke & Devrient. Digitised by Bayerische StaatsBibliothek (BSB), http://bildsuche.digitale-sammlungen.de : viewed 22 April 2017.
It may be possible to confirm family relationships with Johann Georg III by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
However, there are no known yDNA test-takers in his direct paternal line.
Mitochondrial DNA test-takers in the direct maternal line: