NEW YORK—Raj Rajaratnam, a billionaire hedge-fund impresario who built his fortune in the relentless cultivation of corporate contacts, was convicted Wednesday on all 14 counts of securities fraud and conspiracy against him in the biggest insider-trading case ever, likely accelerating an unprecedented wave of prosecutions rocking Wall Street.

The verdict by the 12-member jury, following 12 days of deliberation, capped a blockbuster trial that began in early March and featured 45 wiretaps showing how the founder of Galleon...