WASHINGTON—Senate Republicans blocked law professor Goodwin Liu's appointment to a federal appeals court Thursday, when Democrats fell eight votes short of the 60 needed to end a filibuster.

Mr. Liu, whom liberal legal scholars saw as a rising star, proved more contentious than even President Barack Obama's Supreme Court nominees, as conservative groups mobilized to keep the Rhodes Scholar from joining the San Francisco-based Ninth U.S. Circuit Court of Appeals. Many observers have viewed the 40-year-old Mr. Liu, a former law clerk to Justice Ruth Bader Ginsburg, as a future Democratic Supreme Court candidate.

"Goodwin Liu would have brought sterling credentials, great intellect, and a compelling life story to the bench," White House spokesman Eric Schultz said after the vote. "Unfortunately his nomination today fell victim to persistent and serious misrepresentations of his record."

In a floor speech, Senate Minority Leader Mitch McConnell (R., Ky.) called Mr. Liu "a left-wing ideologue who views the role of a judge not as that of an impartial arbiter, but as someone who views the bench as a position of power."

Mr. Liu declined to comment after the vote.