"It is with heavy heart I share that my wonderful brother, Robert, peacefully passed away tonight. He was not just my brother, he was my best friend. He will be greatly missed, but we will meet again. His memory will live on in my heart forever. Robert, I love you. Rest in peace," Trump said in a statement.
Robert Trump, who at 72 was two years younger than the president, was a business executive and real estate developer.
President Trump made an emotional visit to see his ailing brother on Friday at New York-Presbyterian/Weill Cornell Medical Center before going to his golf club at Bedminster, New Jersey, for the weekend.
The president was expected to attend the funeral, an aide said. He has a busy travel schedule in coming days with plans to visit four battleground states as part of his re-election campaign.
The cause of death was not revealed. Trump told reporters on Friday that his brother was "having a hard time" with an undisclosed illness.
ABC News had reported that Robert Trump was hospitalized in the intensive care unit at Mount Sinai hospital in New York for more than a week in June.
That same month, Robert Trump won a temporary restraining order against his and the president's niece, Mary Trump, to stop her from publishing a tell-all book that offered an unflattering look of the US president and his family.
A state supreme court judge in Poughkeepsie, New York, later denied a request to stop publication and cancelled the temporary restraining order.
Robert Trump had said the book, Too Much and Never Enough: How My Family Created the World’s Most Dangerous Man, would violate a confidentiality agreement tied to the estate of his father Fred Trump Sr, who died in 1999.