HOUSTON — As a teenager, Ted Cruz was an intense and eloquent parser of free-market economics, dazzling Rotary Clubs here in Houston by reciting the Constitution. At Princeton, he was a champion debater and an intellectual leader of a band of conservative students. He was a star at Harvard Law School and clerked for the chief justice of the United States.

But few may have imagined Mr. Cruz, 41, in his newest role, as the Tea Party favorite and Republican candidate for the United States Senate, trading verbal orchids with the likes of Sarah Palin and Glenn Beck. Mr. Cruz earned the nomination on Tuesday in a runoff election after more than a year of sweaty street campaigning, drawing national attention for beating Lt. Gov. David Dewhurst, the more experienced nominee of the Texas Republican establishment.

“I’d have predicted that he would be a professor, not a politician,” said Robert P. George, Mr. Cruz’s adviser at Princeton in the early 1990s. Professor George, a noted social conservative, said that Mr. Cruz stood out even among his Ivy League peers as “intellectually and morally serious,” writing his thesis on the separation of powers.

“But he’s certainly not a shrinking violet,” Professor George quickly added in an interview on Tuesday — to which, Mr. Dewhurst, a wealthy conservative who had the support of Gov. Rick Perry, can attest.