It decided that because of Valieva's age and the "untimely notification of the results" of the failed test - in the middle of the Games and nearly six weeks after she gave the sample - that it would do her "irreparable harm" if she were not allowed to compete.
So, she can take part in the women's event which starts on Tuesday and which she is favourite to win.
But the issue of the failed drugs test will still need to be resolved and no time frame has been given for this.
Under Wada rules, if an athlete's A sample is positive, then they may request that the B sample is tested. It is not yet known whether Valieva has asked for this.
