Einstein might best be described as an agnostic.2 Einstein himself stated quite clearly that he did not believe in a personal God:
"It was, of course, a lie what you read about my religious convictions, a lie which is being systematically repeated. I do not believe in a personal God and I have never denied this but have expressed it clearly." So, the quick answer to the question is that Einstein did not believe in a personal God. However, it is interesting how he arrived at that conclusion. In developing the theory of relativity, Einstein realized that the equations led to the conclusion that the universe had a beginning. He didn't like the idea of a beginning, because he thought one would have to conclude that the universe was created by God. So, he added a cosmological constant to the equation to attempt to get rid of the beginning. He said this was one of the worst mistakes of his life. Of course, the results of Edwin Hubble confirmed that the universe was expanding and had a beginning at some point in the past. So, Einstein became a deist - a believer in an impersonal creator God:
"I believe in Spinoza's God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with fates and actions of human beings."