He was riding high after a landmark federal-court victory — and then apparently got even higher.

A black city firefighter who was one of the named plaintiffs in the bitter court fight to force the FDNY to hire more minorities has been suspended from duty after testing positive for marijuana, sources told The Post.

Firefighter First Grade Kevin Simpkins, 45, began his suspension without pay last Thursday, according to an FDNY document.

Simpkins’ suspension is due to end on Nov. 2, the document said.

He then has been ordered “to report in dress uniform” to the FDNY’s Bureau of Health Services on Nov. 5, and then to the Bureau of Investigation and Trials.

The document did not state the reason for the suspension — which will cost Simpkins about $6,400 in salary, not including overtime he could have earned.

But sources said Simpkins’ sanction stemmed from him failing a drug test that revealed he had marijuana in his system.

Simpkins is a member of the Vulcan Society, which represents black FDNY members.

He is also one of the few individuals named as plaintiffs in the lawsuit against the city in Brooklyn federal court that has compelled a redesign of the FDNY entrance exam and hiring process to get more minorities into the overwhelmingly white department.

The US Justice Department originally filed the suit, but the Vulcans and several individual members, including Simpkins, later intervened in the case as plaintiffs.

Last year, Judge Nicholas Garaufis, in a damning ruling against the city, said a special monitor was needed to make sure the FDNY takes steps to correct the racial imbalance in its ranks, where blacks account for just 3 percent of all firefighters.

The city is appealing the decision, which threatens to cost New York $128 million in damages.

There was no answer when a reporter knocked on Simpkins’ door last night, or when a call was placed to his home.

An FDNY spokesman declined to comment.

Additional reporting by C.J. Sullivan