Data most certainly does NOT follow the three laws of robotics.
Data is a serving officer in the Federation's military, he gives as well as takes orders. If he were to follow the Second Law of robotics, even enlisted personnel could force him to follow their orders.
Data ignores the Third Law, he could not have acted as he did at the end of Nemesis - there were obvious and superior ways to save Picard without risking his own existence (a full rundown is beyond the scope of this answer).
Lastly, if we assume (and I think we MUST, given the context of the stories involved) that the term 'human' in the laws would be changed to 'sentient being' (or something similar, to include Vulcans, Andorians, Tellerites, Orions, etc) Data could not function in his tasks aboard the ship and still obey the First Law.
The Enterprise is a warship. The crew explicitly says so in TNG5x14: Conundrum, when they forget everything but their training. The very purpose of the ship is to explore, seek out new life forms, and be ready to blow the everliving hell out of them if they're a threat.
Constantly in the series, Data serves as ops officer. This position is responsible for (among other things) analysis of tactical situations and enemy technology. He frequently suggests ways to disable or destroy enemy ships when standard tactics or technology is found ineffective. His actions DIRECTLY place the crew into harm's way, and he helps bring harm (and death, so much death) unto others.
Data is not, and cannot be, an Asimovian-style positronic robot, or his positronic brain would have burned itself out long ago (possibly before he left the Academy).