Here's a review of another book which purports to deal with the life and times of Constantine: The Age of Constantine the Great by Jacob Burckhardt.
Don't bother with this one. Burckhardt was a 19th century academic with an ax to grind against Constantine and a mission to rehabilitate the Christian-persecuting Diocletian. He pursues both of those ends with blind and tedious enthusiasm.
The book takes about 240 pages just to get to Constantine at all, as Burckhardt loses his focus amid 60 page digressions on pagan practices in the ancient Mediterranean world.
Perhaps most annoyingly, the modern translator has seen fit to strip out all of Burckhardt's references which makes the book into an unverifiable manifesto as opposed to a serious scholarly work.
There are much better and more accessible works out there on Constantine and his times than this one, such as Constantine and the Christian Empire mentioned below, just to give one example. Or, if you prefer to go straight to the primary source, try: The Life of the Blessed Emperor Constantine: From AD 306 to 337 (Christian Roman Empire Series, vol. 8).