This book covers all his life, from his birth and early life in Virginia, to his death after 2 terms as President. As an Englishman, I'll admit that I don't know much about Washington, but I'm reasonably well read about the subject, and this book answered all the questions, and misunderstandings I had about Washington.
The one thing that this book didn't disabuse me of was my wariness of Thomas Jefferson. This wariness has developed through a bunch of books I've read about the "founding fathers," and this book didn't affect my view of him. That said, it's till a good book.
In short, if you want to read one book about Washington, this is probably as good a book as you'll find