[2] His maternal grandfather, Clement Biddle, was also a military leader, having served under George Washington during the Revolutionary War.

[2] He received a Bachelor of Arts degree in 1821 from the University of Pennsylvania and read law in 1825.

[1] He was confirmed by the United States Senate on April 24, 1858, and received his commission the same day.

[6] Cadwalader first married Mary Binney (1805–1831), daughter of Horace Binney, an Anti-Jacksonian United States Representative known for his public speeches; he founded the Hasty Pudding Club at Harvard.

[7] Together, Mary and John had two daughters, including:[8] Following his first wife's death from complications of childbirth, he married Henrietta Maria Bancker (1806–1889) with whom he had six children, including:[10] Through his eldest daughter Mary, Cadwalader was the grandfather of Mary Cadwalader Rawle (1850–1935),[14] who was married on March 24, 1870, to Frederic Rhinelander Jones (the brother of Edith Wharton); their daughter in turn was landscape architect Beatrix Cadwalader Jones Farrand (1872–1959).