AUSTIN — In a changing of the conservative guard, Gov. Greg Abbott’s longtime associate James D. “Jimmy” Blacklock on Tuesday filled a vacancy on the Texas Supreme Court.

In a joint swearing-in ceremony, Abbott administered the oath to Blacklock while the 12-year justice he is replacing, Don Willett, formally ascended to the 5th U.S. Circuit Court of Appeals in New Orleans. Texas Supreme Court Chief Justice Nathan Hecht swore in Willett, who was President Donald Trump’s appointee.

U.S. Sen. John Cornyn, a former Texas Supreme Court justice who recommended Willett to Trump for a vacancy on the 5th Circuit, spoke after the oath-takings.

Both Willett, renowned as a rare judge who makes frequent use of Twitter, and Blacklock, who has kept a much lower profile, worked for Abbott when the Republican governor was Texas’ attorney general.

Since 2015, Blacklock has served as the governor’s general counsel.

A native of Houston who was active in the conservative Federalist Society at Yale Law School, he filed last month as a candidate for a six-year term on the all-Republican state Supreme Court. Willett’s current term expires at the end of 2018.

In a written statement, Abbott noted that Blacklock helped him file lawsuits on the state’s behalf attacking Obamacare and trying to preserve religious liberty. Blacklock also helped defend the Legislature’s new laws restricting a woman’s right to an abortion, Abbott said.

“Jimmy Blacklock is a principled leader who knows that the role of the judicial branch of government is not to legislate from the bench,” he said.