Donald J. Trump, the presumptive Republican presidential nominee, released a list of potential Supreme Court nominees on Wednesday as part of an effort to quell concerns that he would not select conservative jurists.

The unusual move comes as Mr. Trump is looking to unify the Republican Party behind him and win over critics who remain skeptical about his candidacy. While some Republicans who oppose Mr. Trump have considered supporting Hillary Clinton or sitting out the election, he has regularly reminded them that the future of the Supreme Court is at stake.

After the death of Justice Antonin Scalia in February, critics of Mr. Trump expressed concern about whether he had the judgment to fill vacancies on the court. He had joked about appointing his sister, Maryanne Trump Barry, a federal appeals court judge in Philadelphia, before suggesting that he would look for someone in the mold of Justice Scalia and later promising to furnish some prospective candidates.

Mr. Trump said in a statement that his shortlist was “representative of the kind of constitutional principles I value and, as president, I plan to use this list as a guide to nominate our next United States Supreme Court justices.” The Trump campaign did not share how it settled on the names, but Mr. Trump has previously said that he was seeking guidance from conservative groups such as the Federalist Society and the Heritage Foundation.