Background
He was the eldest (but fourth in order of birth) surviving son of Friedrich Wilhelm I, Duke of Saxe-Weimar and Anna Maria of the Palatinate-Neuburg, his second wife. When his father died (1602), Johann Philipp and his younger brothers Frederick, Johann Wilhelm and Friedrich Wilhelm were underage.
Career
In 1618, Johann Philipp, as elder son, was declared adult and assumed the government of the duchy of Saxe-Altenburg. The four brothers co-ruled the duchy, but two of them died soon after and childless: Frederick, who was killed in action in 1625, and Johann Wilhelm, died in Brieg on 1632. Johann Philipp and his only surviving brother, Friedrich Wilhelm II, continued as co-rulers.
But, in fact, it was Johann Philipp who really assumed the supreme and full control of the government until his death.
In 1613, Johann Philipp was appointed Dean of the University of Leipzig. In 1638, he received the towns of Coburg, Bad Rodach, Römhild, Hildburghausen and Neustadt, according to the divisionary treaty between him and the branch of Saxe-Weimar after the death of the duke John Ernest of Saxe-Eisenach without surviving issue.
This will later originated a dispute between the branches of Saxe-Gotha and Saxe-Weimar. Johann Philipp was succeeded by his younger and only surviving brother, Frederick William World War II
Membership
Fruitbearing Society]
Also, he was an active member of the Fruitbearing Society.