1580s, "person skilled in politics;" see politics + -ian. Especially "one engaged in party politics, especially as a trade; one who promotes the interests of a political party," and thus it quickly took on overtones, not typically good ones: "one concerned with public affairs for the sake of profit or of a clique." Johnson defines it as "A man of artifice; one of deep contrivance."
The notion of enlightened, disinterested, and high-minded service to the state goes with statesman (Century Dictionary notes that "A man, however, would not properly be called a statesman unless he were also of eminent ability in public affairs"). For "student of political science," by way of distinction, politicist (1869) has been used.