John H. Grabill was born to Ephraim and Caroline Grabill in Mount Jackson, Virginia on March 8, 1839. He prepared at the Woodstock and Harrisburg Academies and entered Dickinson College in Carlisle, Pennsylvania in 1858 with the class of 1860. While at the College, he became a member of the Phi Kappa Sigma fraternity and was elected to the Union Philosophical Society. He graduated with his class and returned to the Shenandoah Valley.
In the summer of 1861, Grabill enlisted in Company G of the Thirty-third Virginia Volunteer Infantry then forming in his county. He joined with so many of his extended family, including the commander, that the unit was know as "Grabill's Company." The Thirty-third became a part of the "Stonewall Brigade," and Grabill saw extended action during 1862, most notably at the First Battle of Bull Run. After a year with the brigade, Lieutenant Grabill returned home in July 1862 to raise a company of cavalry among the men of Paige and Shenandoah counties. This unit was organized in the autumn of 1862 as Company E of the Thirty-fifth Virginia Cavalry. It was known more colorfully as "White's Comanches," after its colonel and its vocal manner in the charge. As part of the Laurel Brigade, the 35th fought through the rest of the war, participating in the conflicts at Brandy Station and the Wilderness. The unit also served as rearguard in the retreat to Appomattox Court House. Captain Grabill was mustered out in the spring of 1865.
Grabill returned to Shenandoah county where he was superintendent of schools for thirteen years, from 1870 to 1883. He also served as principal of the Woodstock Academy and edited the Shenandoah Herald. Grabill published local histories, including his own Diary of a Soldier of the Stonewall Brigade. He was active in county veterans groups and during the First World War served locally as a member of the Virginia Agricultural Council of Safety.
Grabill married Mary L. Hollingsworth of Woodstock, Virginia in December 1866. The couple had ten children. John Henry Grabill died on February 28, 1922 in Woodstock, Virginia. He was a week short of his eighty-third birthday.