Donald J. Trump announced on Thursday that he would convert $50 million that he had lent to his presidential campaign into a contribution, fulfilling a pledge he made in mid-May.

The decision appears intended to halt speculation that Mr. Trump might seek to recoup his substantial out-of-pocket costs with donations from supporters, clearing the way for him to adopt a more conventional fund-raising approach for the general election. In partnership with the Republican National Committee, Mr. Trump has been seeking to tap into traditional sources of money, including large and small donors, to bolster his own contributions to his campaign.

The decision was announced by Mr. Trump’s finance chairman, Steven Mnuchin, in an interview with Reuters.

The campaign said in a statement: “After self-funding his primary election, Mr. Trump and the campaign have assembled an exceptional fund-raising operation, which in recent days has been overwhelmed with contributions for the Republican Party.”