No, he shouldn't be pardoned. What he did was illegal. Maybe he'll be pardoned. That will depend on the next administration. Nonetheless, I believe that he was acting in the interest of Americans. Sometimes the "right" thing to do is illegal. But that doesn't mean the law should be nullified for an exception. Still, I do think that whatever punishment is designated for what he did should be balanced with the results that his information produced.
Also,
Has national security really been compromised?
Or has government surveillance decreased since the Snowden incident?
What really has changed since then?