William Henry Seward Jr. (he went by Will in close circles) was born June 18, 1839 to William Henry Seward and Frances Adeline Seward (née Miller) in Auburn, New York. He was the third of five children. His siblings were Augustus Henry Seward, Frederick William Seward, Cornelia Seward (who died in infancy), and Frances Adeline Seward.

Will moved to Albany, New York in 1857 where he was a hardware store clerk. He remained in Albany until 1859, when he moved to Washington D.C. to be his father’s private secretary. In 1860, Will established the banking house of William H. Seward & Co with Clinton D. McDougall in Auburn.

Will joined the 138th New York Infantry (later renamed the 9th New York Heavy Artillery) in August 22, 1862 as a Lieutenant Colonel. In May 1864, Will was promoted to Colonel. On July 9, 1864, Will was injured at the Battle of Monocacy when he fell off his horse. Despite the injury, he remained in the army and was promoted on September 14, 1864 to Brigadier General in Martinsburg, Virginia. Will resigned from the army on June 1, 1865 and returned to Auburn where he resumed banking.

Will married Janet MacNeil Watson on June 27, 1860 in Auburn. The couple had three children, Cornelia Margaret Allen (née Seward), William Henry Seward III, and Frances Janet Messenger (née Seward). Will inherited the Seward Mansion at 33 South Street where he raised his family. On April 29, 1920, Will passed away; he is buried in Fort Hill Cemetery in Auburn.