Mordant had a wife and three children when he enlisted in Co. F 24th Michigan Infantry on August 12, 1862, at the age of 30. He worked as a laborer.
The 24th became part of the Iron Brigade. They entered the Gettysburg Campaign, marching from the Rappahannock River through Pennsylvania, arriving at Gettysburg on July the 1st, 1863. They were immediately engaged. Mordant fell as a musket ball tore through his right side, just 2-inches to the right of his spine. The fierce fighting continued but this was the end of the war for Mordant. He was taken to Summit House Hospital in Philadelphia where he was treated for his injuries.
It took a long time to heal. In January, 1864, he was furloughed for 21 days but ended up back in the hospital after just 5 days. In March, 1864, he was transferred into Company 131st, 2nd Battalion U.S. Veteran Reserve Corps. There he acted as guard around the hospital. He was discharged July 3, 1865, at Philadelphia, Pennsylvania.
Mordant returned home to his family. Another five children were born to Mordant and Sarah for a total of eight. He continued to work as a laborer as long as he could, but had to apply for a pension due to his disability. Eventually, it was granted.
Mordant was a member of G.A.R. 231 Eddy Post in Plymouth. He died at age 79 in 1919, in South Lyon, Michigan.