Born in Trenton, New Jersey, Rellstab read law to enter the bar in 1882.

He was a Judge of the District Court of Trenton from 1896 to 1900, and of the Mercer County, New Jersey Court of Common Pleas from 1900 to 1909.

[1] On May 6, 1909, Rellstab was nominated by President William Howard Taft to a seat on the United States District Court for the District of New Jersey vacated by Judge William M. Lanning.

Rellstab was confirmed by the United States Senate on May 18, 1909, and received his commission the same day.

He assumed senior status on October 10, 1928, and served in that capacity until his death on September 22, 1930, in Lake Placid, New York.