Referring the final decision to Health Secretary Jeremy Hunt, Justice Treacy said Mr Poots had breached the Minister Code by failing to take the issue before the Executive.
Kieran McCarthy MLA said: “This ruling is fantastic news for all who have been fighting the Health Minister’s despicable and irrational decision to ban gay and bisexual men from donating blood.
“Edwin Poots must now seriously consider his position. It has been made legally clear he breached the Ministerial code by using his position to pursue his own agenda, rather than working within the Executive framework.
“He has been badly advised and now has serious questions to answer. Not only has he wasted public funds, but he also acted to prejudice one section of society in Northern Ireland.
“I would appeal to Jeremy Hunt to make reviewing this decision a top priority, finally bringing Northern Ireland in line with the rest of the UK.”