The Republican judge, who was appointed by George W. Bush, stated that the order represents a major challenge to the Trump administration.
The judge declined to stay Trump's executive order and suggested that travel restrictions should be lifted immediately.
The challenge that led to tonight's ruling was brought by Washington state Attorney General Bob Ferguson.
Judge Robart ruled that the states have legal standing to sue, which could help Democratic attorneys general take on Trump in court on issues beyond immigration.
The judge's decision came on the same day that a lawyer for the Trump administration stunned a Virginia federal judge when he admitted that since Donald Trump signed his executive order last Friday, over 100,000 people have had their visas revoked from the seven majority Muslim countries named in the order.
Washington AG Ferguson described the ban and it's resulting effects as unconstitutional...
"Folks who had visas, folks who were allowed to travel were denied that right without any due process whatsoever - that's un-American and unconstitutional... You cannot prefer one religion over another,"
White House spokesman Sean "alternative facts" Spicer released a statement late Friday saying the government...
"will file an emergency stay of this outrageous order and defend the executive order"
Trump has argued that his directive is aimed at protecting America despite the fact that most terror attacks in the US in recent years have been carried out by home-grown militants and none have been committed by citizens from the seven countries named in the order since 1975.