The most important part of the answer is: we know the end of the story. We know that Satan will be thrown in the deepest hell for all eternity at the end of the world (see Revelation 20:10). What comes before that, is not so easy to understand. There are various verses in the Bible about Satan. But it is not always clear to what time they are referring. It is not always clear how literal we should take them; and it is not even always clear which verses are about Satan and which not. Therefore, a wide range of opinions exists among Christians on this subject. This is not very important, as it does not touch on our salvation.
This is how we read what the Bible says about Satan’s ouster from heaven. God’s angels were present when God created the world, as we learn from Job 38:7, where we read that during creation “the morning stars sang together and all the sons of God shouted for joy”. From this we may conclude that Satan had not yet become God’s enemy at creation. Yet shortly after he fell, because he tempted Adam and Eve to sin (Genesis 3).
Through his sin, Satan lost his privileged position as one of God’s angels. Yet he still had access to God in heaven, as we read in Job 1:7: “Now there was a day when the sons of God came to present themselves before the LORD, and Satan also came among them”. Two Old Testament passages are often mentioned as referring to Satan being expelled from God’s presence: Isaiah 14:12-15 and Ezekiel 28:11-19. However, the primary reference seems to be to earthly kings rather than to Satan. So it is safer not to draw conclusions about Satan from these passages.
In the New Testament, Jesus refers to Satan’s fall twice. In Luke 10:17 He says “I saw Satan fall like lightning from heaven”. This is in response to the remark by the disciples that they cast out demons. Most likely Jesus means that the power of Satan is diminishing through the disciples ministering in Jesus’ power, rather than a literal fall from heaven. In John 12:31 He says “now is the judgment of this world; now will the ruler of this world be cast out”. Jesus says here that through His death on the cross, Satan and his kingdom are defeated. It is not clear whether Jesus is talking about a literal casting out of heaven.
Satan is defeated
In Revelation 12, John sees a vision of the rebellion of Satan against God. After a description of how Satan fights against Christ, it says: “Now war arose in heaven, Michael and his angels fighting against the dragon. And the dragon and his angels fought back, but he was defeated, and there was no longer any place for them in heaven” (Revelation 12:7-8). The conclusion of that is that “the accuser of our brothers has been thrown down, who accuses them day and night before our God” (Revelation 12:10). From that it may be concluded that after Jesus broke Satan’s power by providing redemption for sin on the cross, Satan’s power to accuse was broken, and he lost the opportunity to stand before the throne of God like in the story of Job.
In summary, there are three major stages in Satan’s downfall. The first stage was when he rebelled against God and lost his position among God’s angels. The second stage was when Jesus broke his power through his death on the cross and took away his right to accuse the believers before God in heaven. The third stage will be at the end of the world when God will condemn Satan to hell.