He was the son of Johann Georg Birnstiel, a businessman and bank president from Bavaria, and Salome Wälli, a Swiss woman.
He was educated in Latin by a Catholic priest and later attended the Cantonal School in St. Gallen.
In 1881 Birnstiel was appointed as a Swiss Reformed pastor in Schönengrund.
He suffered from a stroke in 1913 and retired from ministry and spent the rest of his life as a writer.
His writing included autobiographies, history books, and religious and theological works.