Born on November 14, 1875 to Fernando H. del Pilar and Felipa Sempio of Bulacan, Bulacan, the fifth among six siblings.
His siblings were  María de la Paz del Pilar (b.1865), Andrea del Pilar (b. 1866), Pablo H. del Pilar (b. 1869), Julian H. del Pilar (b. 1872), and Jacinto H. del Pilar (b. 1878).
He was part of the del Pilar family (more properly Hilario del Pilar; Hilario was the original surname before the Claveria naming reforms and was contracted to "H.") of the principalia, whose members included his uncles, lawyer-turned-propagandist Marcelo H. del Pilar, editor-in-chief of Diariong Tagalog and La Solidaridad, as well as the priest Toribio H. del Pilar, who was exiled in Guam for his alleged involvement in the 1872 Cavite Mutiny.
The del Pilar clan was distantly related to the Gatmaitans.
Although principalia, Gregorio del Pilar's branch was relatively poor.
It was said that del Pilar had to hawk meat pies as a child to survive.

As a child, he completed his primary education under Maestros Monico Estrella and Romualdo Sempio before being sent to study in Manila.
He was enrolled at the Ateneo Municipal de Manila at the age of 15, where he was rated good in Latin, Greek, Spanish and French, middling in philosophy, and excellent in arithmetic and algebra.
During his studies in the Ateneo, he stayed in the house of his fraternal aunt, Hilaria H. del Pilar, and her husband, the propagandist Deodato Arellano.
He helped his uncle distribute revolutionary pamphlets and other materials.
There was one incident in Malolos, where del Pilar stole copies of the book Cuesteones de sumo interes from the parish priest, Father Felipe García, who had a habit of distributing counter-revolutionary materials after mass.
These books were set to be distributed after the mass.
Del Pilar removed the book covers and pasted the pamphlets inside before distributing them after.

Del Pilar finished his bachelor of arts in March 1896 and had intended to enroll at the School of Arts and Trades and study to become a maestro de obras; however when the revolution broke out in August of that year his plans of further study were thwarted.
Del Pilar quickly went home to Bulacan and enlisted himself for military service under Colonel Vicente Enríquez.
Born on November 14, 1875 to Fernando H. del Pilar and Felipa Sempio of Bulacan, Bulacan, the fifth among six siblings. His siblings were  María de la Paz del Pilar (b.1865), Andrea del Pilar (b. 1866), Pablo H. del Pilar (b. 1869), Julian H. del Pilar (b. 1872), and Jacinto H. del Pilar (b. 1878). He was part of the del Pilar family (more properly Hilario del Pilar; Hilario was the original surname before the Claveria naming reforms and was contracted to "H.") of the principalia, whose members included his uncles, lawyer-turned-propagandist Marcelo H. del Pilar, editor-in-chief of Diariong Tagalog and La Solidaridad, as well as the priest Toribio H. del Pilar, who was exiled in Guam for his alleged involvement in the 1872 Cavite Mutiny. The del Pilar clan was distantly related to the Gatmaitans. Although principalia, Gregorio del Pilar's branch was relatively poor. It was said that del Pilar had to hawk meat pies as a child to survive.
As a child, he completed his primary education under Maestros Monico Estrella and Romualdo Sempio before being sent to study in Manila. He was enrolled at the Ateneo Municipal de Manila at the age of 15, where he was rated good in Latin, Greek, Spanish and French, middling in philosophy, and excellent in arithmetic and algebra. During his studies in the Ateneo, he stayed in the house of his fraternal aunt, Hilaria H. del Pilar, and her husband, the propagandist Deodato Arellano. He helped his uncle distribute revolutionary pamphlets and other materials. There was one incident in Malolos, where del Pilar stole copies of the book Cuesteones de sumo interes from the parish priest, Father Felipe García, who had a habit of distributing counter-revolutionary materials after mass. These books were set to be distributed after the mass. Del Pilar removed the book covers and pasted the pamphlets inside before distributing them after.
Del Pilar finished his bachelor of arts in March 1896 and had intended to enroll at the School of Arts and Trades and study to become a maestro de obras; however when the revolution broke out in August of that year his plans of further study were thwarted. Del Pilar quickly went home to Bulacan and enlisted himself for military service under Colonel Vicente Enríquez.
Gregorio del Pilar