[2] He was admitted to the bar and entered private practice in Metropolis, Illinois from 1849 to 1853.

[3] He was reelected from Illinois's 13th congressional district to the 38th United States Congress and served from June 2, 1862, to March 3, 1865.

[3] Allen received a recess appointment from President Grover Cleveland on April 18, 1887, to a seat on the United States District Court for the Southern District of Illinois vacated by Judge Samuel Hubbel Treat Jr.[2] He was nominated to the same position by President Cleveland on December 20, 1887.

[2] He was confirmed by the United States Senate on January 19, 1888, and received his commission the same day.

[2] His service terminated on January 26, 1901, due to his death while on a visit to Hot Springs, Arkansas.