Danny Barak, 48, jumped from his office on the 17th floor of one of Tel Aviv's most prominent office towers on Friday, the spokeswoman said.
Barak, who is survived by his wife and four children, did not leave a note explaining his suicide.
"It is a mystery," the spokeswoman said.
Barak, who founded Leader Capital Markets, was CEO since 2001. He held 15.5% of the company, which is a subsidiary of Leader Holdings & Investments.
"Danny's professional abilities contributed to the establishment of Leader Capital Markets as a leading entity in Israel's capital market," Leader Capital Markets Chairman Yair Fudim said in a statement.
"Danny Barak's death is a heavy loss not just to our group but to the entire Israeli capital market."
Following the recent sale of Leader Holdings to businessman Dan David, Barak was due to step down as CEO in 2011 though he had been offered to stay on as chairman of Leader Capital Markets, the spokeswoman said.
The investment bank is engaged in underwriting, corporate research, securities trading for institutional investors and asset management.
Shares in Leader Capital Markets opened down 5.8% in Tel Aviv on Sunday morning.