Donald Trump will quickly begin to define his presidential legacy by nominating a new Supreme Court justice as one of his first acts in office.

The high court has had a vacancy since the sudden passing of Justice Antonin Scalia in February, despite a strident effort by President Obama to replace the conservative with his own choice, Merrick Garland.

And now the balance of the divided court, where there are four conservatives and four liberals, is in the president-elect’s hands.

“His vision for the court was well expressed in the campaign — justices who will interpret the Constitution based upon its original meaning, which was surely at the heart of the Justice Scalia’s jurisprudence,” former Reagan administration lawyer David Rivkin told The Post.

Trump has committed to nominating conservative justices from a 21-person list he distributed during his presidential campaign.

The list includes: Sen. Mike Lee of Utah, US Court of Appeals Judge Margaret Ryan, Iowa Supreme Court Justice Edward Mansfield, Georgia Supreme Court Justice Keith Blackwell, Florida Supreme Court Justice Charles Candy, US Court of Appeals Judge Timothy Tymkovich, US District Court Judge Amul Thapar, US District Court Judge Federico Moreno and Michigan Supreme Court Chief Justice Robert Young.

Trump could play a major role in shaping the court.

“Now one [Supreme Court opening], but more than that in the next few years. Don’t want to sound ghoulish, but pretty unlikely [Justice Ruth Bader] Ginsburg will be able to stay long with her age [83] and health,” Rivkin said.

“Certainly one, likely two, possibly three,” he said of picks that may be available to Trump in his first term alone.