Paombong High School is the first private secondary school established in Paombong, Bulacan. It is a non-sectarian school for boys and girls. On June 21, 1947, permission of operation of classes was filed in the Bureau of Private Schools. On July 3, 1947, government authority was granted to Paombong High School through Temporary Permit No. 1049 to operate classes of the first three years of the General Secondary Curriculum. On June 28, 1948, the first, second, and third years were recognized by the government. Simultaneous to this Government Recognition of the first three curriculum years, permission to operate the fourth year was filed in the Office of the Director of the Bureau of Private Schools. On March 14, 1950, the school received Government Recognition No. 562 for the complete Academic Secondary Course. Since the receipt of this Government Recognition, Paombong High School has been operating complete classes of the General Secondary Curriculum.

During the first two years of its existence – school years 1947-1948 and 1948-1949 – Paombong High School was housed in three private buildings. Classes were initially held in the Gatchalian building in San Isidro I. After two months, the school moved to the Pasco building located in the same barrio where it stayed until the close of the school year 1947-1948. The following year, the school transferred to the Tan Juan building located at the town proper. A lot with an area of 11,511 sq.m. at the back of the parish church and in front of the public cemetery was rented and eventually purchased by the school owner, Maria Panganiban-Pahati from the late Francisco Marasigan. Here, she built a four-room building which now occupies the area. The school year 1949-1950 gave birth to the present site.

On March 16, 1949, Paombong High School turned out its first batch of graduates, fifteen in number.

The succeeding years saw marked improvement in the school facilities and gradual increase in enrolment. From one four-room building the school site now has eight buildings notable of which are the school canteen, multi-purpose hall named Bulwagang Maria P. Pahati, and a two-storey building which houses the Learning Resource Center in the first floor and the Kitchen Laboratory and the Office of the Society of Leaders in the second floor. Additional classrooms were added to accommodate students who come not only from Paombong but also from nearby towns.

` The following rendered their invaluable services as principals since 1947 until 2001 namely: Mr. Conrado T. Alfaro, Mr. Donato C. Umali, Mr. Cirilo Concepcion, Mrs. Juanita B. Meribeles, Mrs. Socorro B. Ignacio, Miss Avelina P. Gatmaitan, and Mr. Antonio P. Pahati. The office is now presently occupied by Mrs. Marie-Fe P. Santos.

School Year 2007-2008 witnessed the 60th founding anniversary of the institution. It ushered in challenges and opportunities as well. It was also during this school year that the school community prepared for the renewal of its government recognition which saw its fruition on July 16, 2008 when it was awarded Government Recognition No. 029 s., 2008.

The advent of the new K to 12 curriculum brought changes to basic education. Remarkably, ten years became twelve as two more years of Senior High School were added to basic education. 

PHSI responded by offering Science, Technology, Engineering and Mathematics or STEM as its curricular offering in the school year 2016-2017. This year also saw the rise of the Senior High School building, the first installment in a master plan to renovate the campus in the following years.

Today, as revisions in the curriculum for Junior High School and Senior High School are implemented in phases and as we take into account the Programme for International Student Assessment (PISA), we continue to strive to be the pioneer and premier secondary school not only in the town but also in the province.