Answer:

This question plunges deep into a theological conversation that took place around 200 AD among the early church fathers. The conversation has to do with the doctrine of the Trinity. The word “Trinity” is not used in the bible, but the concept spans from Genesis to Revelation. The doctrine goes something like this:

1. God is one, and that there is but one God (Deut. 6:4; 1 Kings 8:60; Isa. 44:6; Mark 12:29, 32; John 10:30). 2. the Father is a distinct divine Person, distinct from the Son and the Holy Spirit. 3. Jesus Christ was truly God, and yet was a Person distinct from the Father and the Holy Spirit. 4. the Holy Spirit is also a distinct divine Person. (M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897)

Yes, God is one, but he is Father, Son, and the Holy Spirit. This may be difficult to get your mind around, and if this is the case, don’t worry. You are not the first person to struggle with this. But to answer the question, the Holy Spirit did exist before Christ’s ascension and was present throughout the Old Testament in various forms. However, the Holy Spirit’s role in the life of the early church was certainly distinct.
The Holy Spirit’s presence can be seen as far back as the Creation story (Gen 1:2). His work is visable in the life of Gideon, Samuel, David and numerous Old Testament people. However, the manner in which the Holy Spirit indwells believers in Acts 2 and following is different.

When Mary is notified that she is pregnant, notice that the Holy Spirit is a part of the process. And this was certainly before the ascension.

This is how the birth of Jesus Christ came about: His mother Mary was pledged to be married to Joseph, but before they came together, she was found to be with child through the Holy Spirit. --Matthew 1:18

But when the Holy Spirit shows up in Acts 2, it is a special event that had been promised from long ago. The Old Testament prophets spoke of a day when the Spirit of God would be poured out in a way that was unparalleled. If you want to read some of these prophecies, you can find them at Joel 2:28ff., Is. 32:15 and Ezk. 36:27. Jesus had told the believers to go and wait for the Holy Spirit to come, something that presumably wasn’t with them yet. So when the Holy Spirit shows up in Acts 2, it is in a way that was quite different from the experience of anyone who had come before.
So I guess the short answer is that the Holy Spirit did exist before Christ’s ascension. But the way in which he came in Acts 2 is unique, powerful, and poured out in a manner that had not happened before. John Stott says about Pentecost

Pentecost was the inauguration of the new era of the Spirit (The Bible Speaks Today)

His (the Holy Spirit’s) role in our life today is a “new era” that began in Acts 2. The third person of the God-head existed before that time, but reveals itself in a new way at Pentecost.

Answered By: Wade