During his early childhood, his parents relocated their family several times, first to Rahway, New Jersey, then to New York City, and then to Delaware, where, as an older child, John Wainwright was encouraged to learn the trade of coach painting.

[6] John Wainwright became one of Pennsylvania's earliest responders to President Abraham Lincoln's call for 75,000 volunteers to help defend the nation's capital following the fall of Fort Sumter to Confederate States Army troops on April 13, 1861.

[9] He engaged with his regiment and other Union forces in the capture of Fort Clinch and Fernandina, Florida in March 1862 and in the operations in South Carolina on James and Edisto islands leading up to the Battle of Secessionville.

Commissioned as a first lieutenant on May 1, 1863 at St. Helena Island, South Carolina, he was detailed from May 10 to June 11 as acting adjutant of his regiment, and was temporarily placed in command of the 97th Pennsylvania's H Company from July 4 to September 7, during which time he participated with his regiment and other Union troops in: the capture of Morris Island, South Carolina; the siege of Forts Wagner, Gregg, Sumter, Moultrie, and Johnson; and the Second Battle of Fort Wagner (July 18, 1863).

[11][12] Participating with his regiment in the Union Army's operations at Camp Cooper, Woodstock Mills and Kings Ferry, Florida during the early part of 1864, and still holding the rank of first lieutenant, he was placed in temporary command of the 97th Pennsylvania's I Company from February 25 to March 27.

[15] Two months later, he received an honorable mention from his superiors for his display of gallantry during the Battle of Chaffin's Farm, Virginia on October 7, 1864 while serving as acting regimental adjutant.

Fighting with the 97th Pennsylvania in that same battle, Wainwright was wounded in the right shoulder by grape shot while performing the acts of gallantry which resulted in his receipt of the U.S. Medal of Honor.

Employed as a dry goods merchant during the 1870s and 1880s, the elder John Wainwright resided with his wife and children in Wilmington, Delaware, and became an active member of the Grand Army of the Republic, as well as a companion of the District of Columbia Commandery of the Military Order of the Loyal Legion of the United States.