NEW YORK — Rajat K. Gupta, the retired head of the consulting firm McKinsey & Co. and a former Goldman Sachs board member, was found guilty Friday of conspiracy and securities fraud. He is the most prominent business executive convicted in a wave of prosecutions that followed the government’s sweeping investigation into insider trading on Wall Street.

After a monthlong trial in US District Court in Manhattan, a jury took only two days to deliberate before reaching a verdict. It found Gupta guilty of leaking confidential information about Goldman to his former friend and business associate, fallen hedge-fund titan Raj Rajaratnam, on three occasions in 2008. He was also convicted of conspiring in an insider-trading scheme with Rajaratnam.