Believing himself called to religious life, he went to Leuven and entered the Congregation of the Sacred Hearts of Jesus and Mary.

He arrived in Honolulu on November 13, 1854, and was subsequently ordained to the priesthood as a member of the Congregation of the Sacred Hearts of Jesus and Mary on May 31, 1862, at the age of 34.

Louis Maigret fell ill, Father Koeckemann was appointed coadjutor vicar apostolic to fulfill some of the bishop's regular duties.

On August 21, 1881, Father Koeckemann was ordained at Saint Mary's Cathedral in San Francisco, California, as a bishop of the titular see of Olba at the age of 53, with a papal mandate to serve as coadjutor[2] Vicar Apostolic with right of succession.

During his episcopate, the massive migration of Portuguese workers for the sugarcane plantations from Madeira Islands and the Azores began.