Edward Grannis was born on November 30, 1838, possibly in Claremont, New Hampshire, to Laurens Grannis and Martha Cole. His father was a farmer who owned at least $3,000 in real estate and $1,000 in personal property by 1860. Edward attended school in Claremont and worked as a laborer on his father's farm. He moved to Guildhall, Vermont, sometime in the early 1860s.
Grannis enlisted in the Union army on September 17, 1862, and mustered into Company G of the 15th Vermont Infantry on October 22. The regiment served in the eastern theater of the war, predominantly helping to defend Washington, D.C. Grannis mustered out in Brattleboro, Vermont, on August 5, 1863. He married Hannah Cordelia Knight on April 11, 1867, and he worked as a farmer in Lancaster, New Hampshire. They had two children: Frederick, who was born in November 1868 and died in March 1873; and John, who was born around 1873 and died in December 1891. Grannis applied for a pension in April 1879, complaining of asthma and chronic diarrhea. He died in Lancaster on April 1, 1913.