James J. Siebeneck was born in Mainz (or Mayence), Germany, on April 11, 1827. His parents were Franz and Clara Siebeneck. He arrived in the United States in 1848 or 1849, at age 21. He initially worked as a civil engineer and surveyor on canal and railroad projects. Siebeneck received his legal education in Towanda, Pennsylvania, where he served an apprenticeship known as reading law in the office of an established attorney between 1855 and 1857. He passed the bar in Towanda in 1857, and came to Pittsburgh in 1857 or 1858. He was listed in the Pittsburgh city directory for the first time in 1858, as an attorney at law whose office was on Grant Street, Downtown. He boarded at a different address on Grant Street.
On October 20, 1859, Siebeneck married Margaret E. Thomson McKinney, who had been born in Tennessee on April 11, 1825. Her parents were Archibald McKinney, born outside the United States and later a Pittsburgh resident, and Ann Watson McKinney, born in Pittsburgh. Ann Watson McKinney, according to information compiled by Allegheny West historian John Canning, was a daughter of Andrew Watson, an early Pittsburgh tavern keeper. James J. and Margaret Siebeneck had two children: James J. Jr., who was born in 1860 and died in infancy, and Clara H., who was born about 1862 and died in 1865.
After marrying, the Siebenecks lived in a boarding house in Wylie Avenue in the lower Hill District, then lived in what was probably their own home on the same street until 1869. During the Civil War James Siebeneck, a Republican like President Lincoln, was a strong Union supporter. He participated in a recruitment rally held on the West Common in Allegheny City on July 24, 1862, and contributed $50 to a bounty fund that rewarded volunteers for enlisting. He was among the speakers on the steps of the Pittsburgh main post office when the war ended three years later. His later participation in public life included serving on the Allegheny County Centennial [of the United States] Committee in 1876 and participating in dedication ceremonies for the new Allegheny County Courthouse in 1888.
The 1870 population census was the first census taken following the construction of 851 Beech Avenue. The census recorded James Siebeneck as an attorney who owned real estate worth $87,000, several times the value of his home, and had a personal estate of $6,500. Margaret, 44, kept house. The couple employed a servant who lived in their home: Mary Chambers, 22, who had been born in Ireland.
Margaret Siebeneck died on September 28, 1877, at age 51. Her death left James Siebeneck living alone at 851 Beech Avenue, except for household staff. The 1880 census enumerated two such residents of the house: Nancy Mcllevein, 66, a housekeeper born in Ireland, and Fanny Davis, 21, a servant who had immigrated from Wales. Records of the 1890 census, which would provide information on all occupants of 851 Beech Avenue in that year, were destroyed in a warehouse fire in Washington D.C. in the 1920s. By that time, Siebeneck had family members at close proximity, as a brother, Pittsburgh newspaper publisher Joseph G. Siebeneck, also a widower, and his family moved to 855 Beech Avenue in about 1887. Both Siebeneck brothers and Joseph’s family were listed in Pittsburgh and Allegheny Blue Books, or social directories, after publication began in the 1880s.
James Siebeneck practiced law on Grant Street and on Wylie Avenue at Fifth Avenue and Grant Street for the rest of his life. He may also have taken some cases in Beaver County, where he became licensed to practice in 1868. He died at home at 851 Beech Avenue on March 20,1896. His heirs sold his house in 1899.