They were married on September 21, 1865, and had the following children: Ella, Sara (also known as Sadie), Joseph, Walter and James.
During the Civil War, McMellen enlisted for service in the Union Army, becoming a private in Co. K, 79th P. V. I., which regiment was assigned to Gen. Negley's brigade.
In 1863 he was mustered out of the 79th Regiment on a surgeon's certificate, and the same year, when his health had somewhat recovered, was again received into the service, as first lieutenant of Co. C, 21st Pa. Cavalry.
McMellen participated in the last charge made by the Army of the Potomac, on the morning of the surrender of Gen. Robert E. Lee.
In this work of building and contracting he was very successful, and many iron, wooden and stone bridges in Lancaster and adjoining counties were erected by him, his reputation as a bridge builder being second to that of no man in eastern Pennsylvania.