Sen. Scott Brown (R-Mass.) said on Thursday that he will vote against confirming Elena Kagan as a Supreme Court justice.

Brown announced early this afternoon that he will vote against Kagan, whose confirmation is all but certain after the vast majority of Democrats and a handful of Republicans have said they would support her.

Brown chalked up his decision to Kagan's lack of experience as a judge.

"I believe nominees to the Supreme Court should have previously served on the bench. Lacking that, I look for many years of practical courtroom experience to compensate for the absence of prior judicial experience," he said. "In Elena Kagan’s case, she is missing both."

Kagan had served as dean of Harvard Law School in Brown's native Massachusetts, and Brown had introduced her along with Sen. John Kerry (D-Mass.), as is customary, at the beginning of Senate hearings.

Brown's decision is notable for what it says about a senator who's sought to carefully manage a centrist record going into a reelection effort in 2012 in a reliably Democratic home state. He has supported some extensions of unemployment benefits and voted for Wall Street reform. But Brown was also a critic of healthcare reform, President Obama's pick for a labor board, and a number of other issues.

"The best umpires, to use the popular analogy, must not only call balls and strikes, but also have spent enough time on the playing field to know the strike zone," he said. "Therefore, I cannot support Elena Kagan’s nomination."