In the Gospels of Matthew, Mark and Luke there is agreement that the Last Supper was the Passover meal (Matthew 26:17-20, Mark 14:12-17, Luke 22:7-15) after which Jesus was taken prisoner and finally condemned to death. In the Gospel of John this last meal takes place over chapters 13-17 and seems to be prior to the Passover meal (John 13:1). In John's Gospel, it seems that Jesus was taken prisoner prior to the Passover meal and Peter's denial of Jesus occurred prior to the Passover (John 18:28). In fact, the Gospel of John seems to have the crucifixion occurring on the same day the Passover lamb was slain (John 19:14), but this is not in unity with the other gospel accounts. However, we know there are no contradictions in the Bible. Therefore, we need to understand what John was referring to in his account of Jesus' crucifixion. We must look at the facts presented and reason these together to establish harmony in all the Gospels.
To begin, we see that the Gospels of Matthew, Mark, and Luke state that it was the first day of unleavened bread. In Matthew 'Feast of ' is not in the original text and Mark and Luke state specifically that it was the day of unleavened bread in which the Passover Lamb was slain. This is explained by understanding that unleavened bread was also eaten with the Passover meal on the fourteenth day of the first month (Ex. 12:8). Therefore, it was the first day in which unleavened bread was eaten. However, following the one-day Feast of the Passover, the Feast of Unleavened Bread continued as a seven-day feast from the fifteenth of the month until the twenty first day (Lev. 23:4-8). During this feast an offering made by fire was done each day. Since this would be a total of eight days, the Lord's Sabbath would also occur during this time. Therefore, not only would the usual sacrifice be done on the Sabbath but also the one done during the seven-day feast. This explains why John calls this Sabbath a 'High Day' (John 19:31). Furthermore, we need to understand that sometimes all days were called 'the Passover' (Luke 2:41; 22:1; Acts 12:3-4) or the seven days were the 'Passover Week' (John 18:28; 19:14). Also, the Sabbath, the day of rest, was on a Saturday. Concerning John 19:14, "the day of Preparation" does not mean the day of preparing for the Passover. In the first century "the day of Preparation" meant "the day to prepare for the Sabbath" -- in other words, Friday. It is this usage which is relevant in John 19:14. Thus, "the day of Preparation of the Passover" means "the Friday of Passover week." John is referring to the Preparation Day before the Sabbath and states this clearly in 19:31. By this reasoning all the gospels will be in agreement. Therefore, the Last Supper was Passover night, and Preparation Day of the Sabbath was the next day in which Jesus was crucified.
Jesus foretold His disciples that He would suffer, die, and then rise from the grave on the third day (Mk. 8:31; 9:31; Lk. 24:46). Here, Jesus is referring to the time from when He would begin to suffer to the time He would arise from the grave. Passover night (Thursday) began His suffering. This was the first day in which He was arrested and rejected by the elders and priests. The next day, Friday, was the second day in which He was beaten, mocked, scourged and killed. Saturday, the Sabbath and third day, He remained in the grave. Sunday morning, the first day of the week, He was already gone from the grave. For those who try to get three days and three nights to fit what Matthew records in 12:40, it can still work for them. As Jonah had no control on his fate for three days and three nights but God watched over him, Jesus was in the hands of the elders and priests for three days and three nights, but God watched over Him. Thursday evening to Saturday evening was three nights. Early Friday morning to early Sunday morning was three days.