He will head Shareholder Engagement and M&A Capital Markets for North America and will be based in New York, the sources said.
Porretti was previously head of Shareholder Advisory at independent investment bank Greenhill & Co, and before that worked at Morgan Stanley on the bank's shareholder activism and corporate defense team.
He is a lawyer and began his career at Cleary Gottlieb.
JPMorgan declined to comment.
The move comes after two executives working on activism defense left the bank. Benjamin Wilson, who had been responsible for North America, left in February to join another firm, and Kirshlen Moodley, who had been head of the practice in Europe, Middle East and Africa, left in late 2020.
JPMorgan had restructured its shareholder advisory business several months ago with David Freedman, a veteran dealmaker, who was tapped to lead the global shareholder engagement and M&A capital markets group.
Activism defense has become a major franchise for investment banks, as hedge funds such as Elliott Management, Starboard Value and Third Point push for changes at companies.
While the COVID-19 pandemic tamped down activist campaigns last year, the pace is picking up now with a number of investment firms pressing for strategic reviews to consider M&A and demanding board refreshments. Several firms have nominated directors to boards at companies ranging from Exxon Mobil (XOM.N) to OneSpan (OSPN.O).
There has also been movement among bankers in the last months. In January, UBS hired Aneliya Crawford from law firm Schulte Roth & Zabel LLP to co-head its activism defense group.
