LONDON — President Jacob Zuma of South Africa suffered a stinging legal defeat on Wednesday when the country’s High Court rejected his efforts to block an inquiry into accusations of influence-peddling so widespread that it is known as “state capture.”

The decision came days before a major gathering to choose Mr. Zuma’s successor as leader of the governing African National Congress. After the findings were read aloud in court, the public gallery burst into applause and cheers, according to local news media reports.

The allegations center on accusations that Mr. Zuma has been complicit in a scheme by three businessmen that allows them to influence the appointment of government ministers in order to tilt the awarding of contracts in their favor.

Mr. Zuma and the men, who are brothers, have all denied the charges.

The court’s judge president, Dunstan Mlambo, said Mr. Zuma’s conduct in seeking to gag an official report into corruption and to block a judicial inquiry “amounts to clear abuse of the judicial process.” The judge also called Mr. Zuma’s challenge “ill-advised and reckless.”