Patrick was born on the 6th of May, 1844, in Ireland and after emigrating to the United States, he joined the US Navy in Baltimore, Maryland. He served during the American Civil War and it was his actions on two separate occasions and vessels that would earn him two Medals of Honor. The citations read:

First Award

Served as boatswain's mate on board the U.S.S. Wyandank during a boat expedition up Mattox Creek, March 17, 1865. Rendering gallant assistance to his commanding officer, Mullen, lying on his back, loaded the howitzer and then fired so carefully as to kill and wound many rebels, causing their retreat.

Second Award

Served as boatswain's mate on board the U.S.S. Don, 1 May 1865. Engaged in picking up the crew of picket launch No. 6, which had swamped. Mullen, seeing an officer who was at that time no longer able to keep up and was below the surface of the water, jumped overboard and brought the officer to the boat, thereby rescuing him from drowning, which brave action entitled him to wear a bar on the medal he had already received at Mattox Creek, 17 March 1865.

Not much else is known about Patrick other than he was married to Emma and had two sons, Edward and William. Patrick Mullen died on the 14th of February, 1897 at the age of 52 and is buried with his wife in the New Cathedral Cemetery in Baltimore, Maryland: Section K-57, grave 2.