Neuroscientist Benjamin Libet has done pioneering experiments which provide the best evidence available with regard to the question of free will. He's one of the first scientists to study the subjective experiences of conscious awareness and correlate them with activity in the brain. In his best known experiment, he showed that before a voluntary action let's say a person decides to flick their wrist—there are telltale signs in the brain of their action 1/2 second before the person realizes they've even made a decision. Libet seems to have proven that the conscious will does not in fact initiate action. Libet has shown, however, that there is a "conscious veto" or what some call "free won't" by which our mind can inhibit action proposed by our subconscious. There is a short window of around 1/10 of a second after an idea becomes conscious in which a person can squelch it. Otherwise, it procedes.
Libet has shown that, in general, it takes about 1/2 second for information in our environment to become conscious. The half-second seems to be required to get a critical mass or neurons to work in synch on a single problem. We can react quicker than that—athletes do that frequently—but these reactions are pre-programmed and occur without conscious awareness. Baseball players, for instance, are not consciously aware of the arc of a pitch. They swing on instinct developed through practice. Also, when we speak, we generally are not aware of the words we are about to say, but rather have the gist in mind, and allow our unconscious to come up with the words.
Libet started out as a materialist, but after many years in the lab, he's concluded that what's known of the physical world cannot account for consciousness. The notion that the mind is reducible to the brain is, in his view, an unproven hypothesis.
Libet also argues that it is meaningful to speak of the "unconscious mind." Many who argue that consciousness is not reducible to the brain would nevertheless accept that the unconscious is reducible to the brain. Libet, however, seems to regard some of the unconscious as pre-conscious, just outside peripheral vision, needing only attention to make it conscious. I remain skeptical as to whether "unconscious mind" is useful terminology.