Allen was left to take care of himself from the age of eight and apprenticed himself to a brick-maker in London for four years before enlisting in the Royal Navy at age twelve (two years short of the legal age). Once he was put to sea he served in the East Indies and in England's second "Opium War" with China. After leaving the service he was given command of the Dolphin, a 140-ton sailing ship that carried cargo through the pirate-ravaged waters between Ningbo and Shanghai. He prevailed in numerous engagements, and for a time carried a charter from the British consul and a complement of marines to hunt down pirates.
Allen eventually gave up sailing and joined General Charles Gordon's "Ever Victorious Army" as an ensign in command of Chinese troops. He was soon promoted to lieutenant, and then to captain, commanding Company I of the 3rd Regiment through the remainder of the Taiping Rebellion. After the army disbanded in 1864 he involved himself in contracting and building. He married the former Ellen Baker, also a native of England, in October 1869.
Contacted by an uncle living in western New York, Allen emigrated to the United States in 1873. He made his way to Milwaukee, Wisconsin where he was appointed inspector of sewers and later promoted to superintendent of public works. He left to supervise the construction of the Milwaukee & St Louis Railroad's shops. In 1879 he moved to Memphis, Tennessee to oversee construction of a sewer system there, then made his way to New Orleans, Louisiana, where he was responsible for the construction of numerous important buildings.
New Orleans mayor Joseph Shakespeare and architect William Freret introduced him to the industrialists and developers of Birmingham and Allen relocated to the Magic City in February 1886. He immediately contracted for a large number of major developments, including Temple Emanu-El, the Caldwell Hotel, and the Caldwell-Milner building. Allen was a pioneer in the use of construction lifts and other modern labor-saving methods, enabling him to complete projects more expeditiously than his peers.
Allen also served as sanitary officer for the City of Birmingham, at a pay of $100 per week. He submitted his resignation to Mayor B. A. Thompson in August 1889 after engaging in two fights with a contractor named McPollard. In the course of the next decade he was beset by injuries, losing the use of one leg after falling beneath the wheels of a train, and twice being thrown from his horse-drawn buggy.
- Dubose, John Witherspoon (1887) Jefferson County and Birmingham, Alabama: Historical and Biographical Birmingham: Teeple & Smith, Publishers; Caldwell Printing Works.
- The Weekly Age-Herald (August 7, 1889), Vol. 2, No. 32, p. 8
- The Weekly Age-Herald (March 15, 1898), Vol. 24, No. 22, p. 3