Like his father, Mariano , General Alvarez was one of the most valiant generals of the Revolution. He was born on July 25, 1872 in Imus, Cavite. He was an only child. Shortly after his birth, his parents moved to Noveleta, a town on the northwestern part of the province, along the coast of Manila Bay where young Santiago grew up.
He began his early education at the age of seven in a private school in Noveleta under the tutorship of Sr. Antonio Dacon. At the age of ten, he transferred to another private school in Cavite, Cavite, (now Cavite City) where his tutor was Don Ignacio Vilocillo. From there, his parents sent him to Manila because they wanted him to become a teacher. He enrolled at a school conducted by Don Macario Hernandez along Camba street in Tondo. His studies were interrupted by the outbreak of the Revolution in 1896. As soon as peace was restored, he enrolled at the University of Santo Tomas. Subsequently, he transferred to the Colegio de San Juan de Letran where he finally obtained his Bachelor of Arts degree. He then took up law at the Liceo de Manila.
Shortly before the outbreak of the Revolution in 1896 Santiago was made delegado general of the provincial council of the Katipunan in Cavite. When the Revolution spread in Cavite he was promoted to captain-general and later commander-in-chief of the Magdiwang forces. As such, he was among the first in Cavite to take up arms against Spain. All through the Revolution he fought side by side with his father.
Together with his father and with his cousin, Gen. Pascual Alvarez, he was greatly responsible for seizing Novelta from the Spanish civil guards on August 31, 1896. During that encounter, the two Spanish officers were killed and all the civil guards taken as prisoners. The revolutionary forces also seized 29 firearms. Four days later, when the Spaniards attempted to retake the town, the Alvarezes once more shared leadership in their successful defense of Noveleta.
A daring combat soldier, Santiago displayed extraordinary courage and bravery in various assaults on the neighboring coastal and interior towns near Noveleta, specifically Naic, Maragondon, Magallanes, Tanza, Alfonso, Silang, Imus, and San Francisco de Malabon (now General Trias.)
In September of 1896 and under the command of his father, Santiago and Colonel Inocencio Salud took charge of the construction of the ingenious bamboo fortification in Dalahican, a strategic barrio guarding the mouth of the isthmus of Cavite.
From November 9-11, 1896, he engaged the Spanish troops led by General Ramon Blanco in a 36-hour battle in Dalahican. It was one of the bloodiest encounters during the early days of the Revolution. He scored a decisive victory and finally repulsed them. He forced them to retreat, thus, preventing the enemy forces from making a breakthrough into the other towns in Cavite. In this battle he suffered a severe bullet wound on his head on account of which he was forced to rest for more than a week.
At this furious encounter, Santiago ordered his men to dig three huge wells. These wells were made to contain the more than one thousand enemy casualties and a few revolutionary troops that fell. General Artemio Ricarte and General Pascual Alvarez were able to repulse the enemy attacks against Dalahican for more than a year. In this manner, they were able to check every possible effort to send reinforcements from Manila.
Santiago was also known as Kidlat ng Apoy because of the flaming courage he demonstrated as commander of Cavite's famed Batteries 1, 2, and 3 in the battle of Dalahican. He showed this trait once more at the Tejeros Convention of March 22, 1897. During that gathering he almost came to blows with Antonio Montenegro, a Magdalo. Montenegro had raised issued with "touched off' a sensitive spot in the hearts of the Magdiwang members.
As a fitting reward for his exceptional bravery in the battle of Dalahican, he was popularly acclaimed the "Hero of the Battle of Dalahican."
Upon the establishment of the American civil government in the Philippines in 1901, Santiago assisted Pascual H. Poblete, Lope K. Santos, Macario L. Sakay, and many others in the organization of the Nacionalista Party. Like his fellow party members, he aimed to secure for his countrymen, in an opportune time, the independence of his country under the guidance of the United States of America.
In 1902, Governor William Howard Taft named him the presiding officer of the Great Council of Peace Commission (Junta Magna de la Comision de la Paz which was created to expedite the rehabilitation of the country from the ravages of war.
He also collaborated in the founding of the Philippine Independent Church and became one of its leaders. In 1912, he organized the "Makabuhay Association" whose aims were fraternity and mutual assistance.
Santiago was married to Doņa Pat Granados of Tanza, Cavite with whom he had ten children, namely, Marta, Magdalena, Gabriel, Pacita, Numeriano, Egmidio, Rosendo, Virginia, Amelia, and Fidel.
He was only 58 when he died of paralysis on October 30, 1930 in San Pablo, Laguna. His death came just 17 days after his wife died. His remains were buried at the San Pablo municipal cemetery.