Ms Trump, 55, is the daughter of President Trump’s elder brother, Fred Trump Jr, who died in 1981.
The book claims to reveal “a nightmare of traumas, destructive relationships, and a tragic combination of neglect and abuse”.
Robert’s Trump lawyer, Charles Harder, cheered the ruling, saying that “the actions of Mary Trump and Simon & Schuster are truly reprehensible”.
“We look forward to vigorously litigating this case and will seek the maximum remedies available by law for the enormous damages caused by Mary Trump’s breach of contract and Simon & Schuster’s intentional interference with that contract,” Mr Harder said.
“Short of corrective action to immediately cease their egregious conduct, we will pursue this case to the very end.”
Earlier this month, President Trump said that his niece was violating her non-disclosure agreement (NDA) by writing a book.
“She’s not allowed to write a book,” he told Axios, referring to a 20-year legal document she reportedly signed following a dispute over her father’s estate following his death in 2001.
Mr Trump called the NDA a “very powerful one,” adding, “It covers everything.”
What does the book say?
The book was scheduled to hit shelves only weeks before the Republican National Convention, where Mr Trump will accept his party’s nomination to seek a second term.
The memoir will reportedly reveal how Ms Trump supplied the New York Times with confidential documents to print a sprawling investigation into Mr Trump’s personal finances.
The Pulitzer Prize-winning exclusive alleged the president had been involved in “fraudulent” tax schemes and received more than $400m (£316m) in today’s money from his father’s real estate empire.
A lawyer for the president and the White House denied the allegations of fraud and tax evasion made against Mr Trump.
An Amazon blurb for Ms Trump’s book says the author will set out how her uncle “became the man who now threatens the world’s health, economic security and social fabric”.