Siebecker was born in the town of Sumpter, in Sauk County, Wisconsin, the son of recent German American immigrants.

[1] Siebecker was appointed Judge of the 9th Circuit of Wisconsin Courts by Governor William D. Hoard in January 1890.

[2] At the time, the 9th Circuit was composed of Columbia, Dane, Marquette, and Sauk counties, with court proceedings held in Portage, Madison, Montello, and Baraboo, respectively.

[3] Judge Siebecker won the election to the Supreme Court for a term beginning January 1904, defeating J. G. M. Wittig and William Ruger—who had attempted to withdraw his name from the race.

[4] Since the seat was already vacant, Governor La Follette—Siebecker's brother-in-law and former law partner—appointed him to join the court early almost immediately after the election.

In addition to his judicial career, Justice Siebecker was a member and curator of the State Historical Society of Wisconsin.