His father was Dr. George McClellan (1796–1847), a noted ophthalmologist and founder of Jefferson Medical College in Philadelphia. The senior George )son of James and Nancy Eldridge McClellan) married Elizabeth in 1820 in Philadelphia. The couple had four other children: Frederica, John, Arthur, and Mary.
He attended schools their including college. He attended the University of Pennsylvania for two years. He entered the US military academy in 1842 where he excelled. In 1850, he lived in the Philadelphia Dock Ward, according to the Census. He was a great Union general during the Civil War, a railroad owner, a politician and even a one term Governor of New Jersey.
Military service was no stranger to the McClellan family. George was the great-grandson of Revolutionary War general Samuel McClellan (and his wife Rachel Abbe) of Connecticut.
McClellan passed on 29 October 1885 in New Jersey. He is buried in the Riverview Cemetery in Trenton, NJ.