“And they came to life and ruled as kings with the Christ for a thousand years.”
Revelation 20:4

Question:
“How long is Christ’s Reign?”
Some people call this “Christ’s Millennial Reign” but this is not quite accurate.
Our Lord’s reign begins at our rescue with his coronation at Revelation 5:13. Thereafter is a period which encompasses many events: the riding of the three adverse horsemen of the Apocalypse, the bowls of God’s anger, the trumpet blasts, the fall of “Babylon the Great”, Armageddon and the devil’s consequent imprisonment. These events consume most of the Book of Revelation up to chapter 20:4.
Thousand Year Reign
At this point, Christ will rule for a further thousand years with faithful people elevated to Heavenly life, and these ones will act as kings with him. Their reign will be over those remaining of mankind those who have not followed the rebellion, a reign completely free of the devil’s presence. Having been imperfect humans themselves, they will help to guide the faithful on the road to life in this period freed from distress.
On Into Life
When that 1,000 year reign has ended, the devil will be released back to the earth (Revelation 20:7) and being unrepentant, will draw away as many of the cleansed Mankind as he can. However, to protect the faithful and His purpose, God will destroy the devil and those who follow him. Revelation then describes the peaceful transltion to life under Jehovah Himself as Christ hands the earth back to His Father.
Christ’s “Millennial Reign” therefore, is that thousand years in union with those elevated to Heavenly life, a period when the evil forces have been imprisoned and Mankind is able to progress peacefully along the road to Life. However although we know the events which precede and close it, we do not know how long our Lord’s complete reign will last for.