What prompted Judas to betray Jesus? How did Judas's betrayal of Jesus unfold?

TL;DR:

Judas was prompted by Satan and his own selfish ambition to betray Jesus. Judas's betrayal was part of God's plan for Jesus to give His life as a ransom for many.

Although we are not exactly told why Judas betrayed Jesus, it is clear that his motives were selfish. As the treasurer for the disciples, Judas regularly stole from their funds. The Gospels suggest that his desire for financial gain led him to accept thirty pieces of silver from the Jewish leaders to betray Jesus. Additionally, Judas may have become disillusioned with Jesus's mission. This can be seen when he called Jesus "Rabbi" rather than "Lord," implying a lack of true belief in Jesus as the Messiah. This combination of greed, potential disillusionment, and failure to truly accept Jesus likely drove Judas to commit his infamous act of betrayal. Despite Satan’s plans and Judas’ own desires, his betrayal ultimately fell into God's plan for how Jesus would give His life as a ransom for many.

from the old testament

Judas betraying Jesus is not mentioned in the Old Testament.

from the new testament

The disciple Judas is first mentioned by name in Matthew 10:4: "…and Judas Iscariot, who betrayed [Jesus]." Throughout all of history, this is how he is known. Although we cannot know exactly what motivated Judas to betray Jesus, the Gospels do give us clues.
John 6:70–71 says that Jesus knew Judas would betray Him. Even knowing this, He still chose Judas as a disciple and kept him near. The Bible doesn't say why, other than Jesus knew that God had a plan.
John 12:3–8 tells us that Judas loved money. When Mary of Bethany used a bottle of expensive perfume to honor Jesus's coming sacrifice, Judas criticized her for spending it foolishly instead of selling it and donating it to the disciples to feed the poor. However, Judas had no intention of giving it to the poor; Jesus could feed thousands with a few loaves of bread. Judas was the treasurer for the disciples, and he would steal from the cache regularly.
The disciples knew that the Jewish leadership wanted to persecute Jesus—they even warned Jesus to stay away (John 11:7–8). Yet, Matthew 26:14–15 and Luke 22:3–6 reveal that Judas, indwelt by Satan himself, went to the chief priests, offering his services to help them take Jesus under custody. The word translated "betray" actually means to deliver or to cause one to be taken. For whatever reason, the chief priests needed inside help to catch Jesus in a vulnerable position, away from the crowds.
From Matthew 26:21–25, Luke 22:14–23, and John 13:21–30, we see Judas leaving to betray Jesus. There is a bit of confusion over whether Judas was present during the institution of Communion. Which was first, Communion or Judas's departure? Matthew and Mark say Communion came after Jesus's identification of His betrayer but don't mention when Judas left the table. John mentions Jesus's identification and Judas's departure but not Communion specifically. Only Luke writes that Jesus identified Judas after or during Communion—and makes it clear that the betrayer was present at Communion in Luke 22:21. In John 13, Jesus predicts that His betrayer would "eat His bread." He gives Judas a "morsel" (verses 18, 26), which may mean the bread of Communion. It is known that Matthew was organized by subject, not chronology. Luke is generally quite chronological (see the book of Acts). It's possible that Jesus and the disciples discussed His betrayer more than once during the evening, but Judas left after Communion.
In Matthew 26:25, when the disciples tried to discover the identity of Jesus's betrayer, Judas's response was, "Is it I, Rabbi?" It is interesting to note that while the other disciples called Jesus "Lord" (Matthew 26:22), Judas used the word for teacher/mentor. Once Jesus identified him, Satan re-entered Judas. Jesus released him to do what he needed to do, and Judas left the Upper Room.
Matthew 26:47–50 writes that after Judas left the Upper Room, he returned to the authorities who were preparing to take Jesus. He led the large, armed group to the Garden of Gethsemane, and, perhaps because of the low light, identified Jesus with the kiss of a friend.
In Matthew 27:3–10, we see that Judas regretted his part in Jesus's capture. He tried to return the money, but the priests refused to take it. Judas threw the money into the temple and hanged himself.

implications for today

Would Jesus have forgiven Judas? Absolutely. Judas betrayed Jesus, but Peter denied Him (John 18:25–27; 21:15–17). Peter was forgiven and restored. Romans 8:38–39 promises that nothing, including principalities or sin, can keep us from God's love in Christ Jesus. In John 17:12, Jesus identifies Judas as the "son of destruction"—the man doomed to damnation. Judas was an apostate. He had traveled with Jesus, seen the miracles, and heard the teaching, but he didn't believe that Jesus was the Messiah. He called Jesus "teacher," not Lord. First John 2:19 describes him perfectly: "They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us." Judas went out with Jesus, but he didn't follow Him. He understood what Jesus was saying, but he didn't accept it. Such a person, wrapped in apostasy, is doomed to destruction. Acts 1:25 insists that Judas was not forced, but "turned aside to go to his own place." Judas regretted his selfishness, but he still couldn't accept Jesus as Lord.

Countless people today do the same thing. They hear about Jesus's healing power or His ability to grant "wishes" or comfort. Many even respect His teaching, and they learn about His character, His claims, and His crucifixion. However, they don't accept Him as Lord. Ultimately, Judas's story urges us to turn to Jesus as Lord, not following our own selfish ways that lead to death.

understand

Judas's love for money led him to betray Jesus for thirty pieces of silver.
Judas was influenced by Satan to offer his help to the chief priests in capturing Jesus.
Judas regretted his actions, tried to return the money, and ultimately hanged himself out of despair.

reflect

In what ways do your personal ambitions and desires affect your relationship with others and with God?
How do you handle feelings of regret and remorse for your actions, and do you seek forgiveness and reconciliation?
What steps can you take to ensure that your motivations and actions align with your faith and God's Word?

engage

How can we guard ourselves against the influence of greed and selfish ambition in our daily lives?
What can we learn from Judas's betrayal about the importance of truly believing in and committing to Jesus as Lord?
How can we support each other in staying true to our faith and avoiding actions that lead to regret and despair?