Gibson Hood was born around 1841 in Pennsylvania to William and Mary Hood. His father was an Irish immigrant and a farmer who owned $1,200 of real estate in 1850. He grew up and attended school in Greene, Pennsylvania, and his father probably died in the 1850s. By 1860, he was working as a farmer.
He enlisted in the Union army on August 14, 1862, and he mustered in as a private in Company H of the 140th Pennsylvania Infantry on August 22. The regiment took part in the Battle of Chancellorsville, the Battle of Gettysburg, the Overland Campaign, the siege of Petersburg, and the Appomattox campaign. He was promoted to corporal on October 24, 1864, and he mustered out on May 31, 1865.
He returned to Green after the war, and he married Martha Matilda Kennedy. They had at least two children: David, born around 1868; and Jennie, born around 1872. He resumed his work as a farmer, and by 1870, he owned $4,000 of real estate and $1,000 of personal property. He died on December 11, 1871.