Ivanka Trump, President Donald Trump’s daughter, is closing her namesake fashion brand and planning a longer-term focus on policy in Washington.

Ms. Trump, who formally separated herself from the business more than a year ago, holds an undefined policy portfolio as a senior adviser in the White House, most recently centered on workforce development. Her decision to concentrate on the White House comes after months of speculation about whether she and her husband, fellow White House adviser Jared Kushner, would remain in the...