As early as the 2nd century, Christians fasted a short fast on Friday and/or Saturday prior to Easter Sunday as a special Paschal fast in preparation for Easter.
This fast was complete abstinence from food or drink, a sorrowful fast at the absence of the Bridegroom (Mark 2:20)
By the 3rd century, this paschal fast had been extended to embrace the entire week from Monday to Saturday.
There was no uniformity of practice, and some Christians fasted to less than the six full days.
In some places, it was the practice to eat only bread and salt, with water at the 9th hour (3 pm) on the four days (M-TH) and then total fast on Fri-Sat (if possible)
The early church used to celebrate Pascha once every 33 years. However, because some people dies without ever celebrating the feast, the Church decided to celebrate it once a year.
The structure of Holy Week, Pashcal Vigil, and Pentecost was preserved from the establishment of Dionysius of Alexandria (14th Pope of Alexandria 248-264)
Initially, there was some discrepancy between the Church of Antioch (which celebrated Easter on Passover, the 14th of Nissan, even if it was not a Sunday) and the Churches of Rome and Alexandria (which set Easter as the Sunday following the Passover).
The council of Nicea resolved this by setting it's date as the latter.
Although some people believe that the entire Bible was read during Holy Week, most scholars believe that the entire New Testament was read with a special focus on the gospels.
Pope Demetrius (12th Patriarch of Alexandria) took interest in establishing a fixed bases for fasts and Christian holy days. He appended the Holy Fast to the Passion Week.
4 of the 5 Churches (Alexandria, Jerusalem, Antioch, and Constantinople). Church of Rome switched to the Gregorian calendar in the 16th Century
The first official selection of readings seem to be made by Pope Gabriel (70th Patriarch from 1131-1145) who selected some of the prophesies from the OT, Psalms, and NT that memorialized these events in the last week of His Ministry. He then distributed them among the daily hours and compiled it into the Holy Pascha book.
Gathered better readings - tried to make the reading lengths in each hour similar - published it in a Pascha Lectionary - added sermons, many of which from Abba Shenouda the Archimandrite, whose monastery this bishop was from. (This explains why we see so many writings of Abba Shenouda the Archimandrite in the Pascha services.)
Arranged for 4 gospels to be read in entirety. Matthew Tuesday, Mark Wednesday, Luke Thursday, John Saturday
Established reading of all psalms after Good Friday
Composed tunes for many of the prayers. “Adribic” tune came from the monks of mount Adribah, where Abba Shenouda monastery. “El Lahn el Shamy” (Pekethronos for example) came from Mount Shamah, west of Luxor, where the monastery of martyr St. Tawardos was located.