He and two colleagues formalized a plan in which computer transactions could replace shouting traders and mountains of paper records.
Mendelson - along with securities consultant Junius Peake and computer finance whiz R.T. Williams Jr. - presented the plan to the Securities and Exchange Commission in 1975.
"Some Luddites argued we were going to kill the NYSE, put many specialists out of business, and ruin the U.S. financial system," Peake told The Philadelphia Inquirer on Monday from his Colorado home.
Their idea took root in the 1980s, when the stock exchange began to computerize its operations, revolutionizing the industry.
Mendelson later became a consultant to the SEC, the Justice Department and several foreign exchanges.
Before moving to Penn's Wharton School in 1961, he taught at the Massachusetts Institute of Technology and at Harvard, Cornell, and Pennsylvania State universities. He retired in 1994 but continued to teach.
Mendelson was married to the former Ruth Grotsky, who died in 1972. Survivors include their two children.
Mendelson's death was confirmed by the Joseph Levine & Sons Funeral Home in Broomall. Services are scheduled for Thursday at the funeral home.