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 administration for the rest of Mr. Trump’s term.

Apparel sales at the brand, which Ms. Trump launched in its current form in 2014, soared in the year of the 2016 presidential election. But the company also became a lightning rod for critics of her father’s policies, with one anti-Trump group last year urging shoppers to boycott stores selling Trump-branded goods. Retailers including Nordstrom Inc. and Hudson’s Bay have stopped selling Ivanka Trump products in the past 18 months, citing poor sales.

Abigail Klem, who took over as president of the New York-based brand in the spring of 2017, told its 18 employees Tuesday the company would be shutting down. Ms. Trump addressed the staff in person later in the day.

Ms. Trump said she had contemplated the move in recent months as she grew frustrated by the restrictions she placed on the company, IT Collection LLC, to avoid possible conflicts of interest while serving in the White House.