O'Hanley will work with Powers for a transitional period and reports to Jay Hooley, State Street's chairman and CEO.
State Street Global Advisors is the investment management arm of Boston-based State Street Corporation, and manages substantial assets for insurance companies, as well as for other institutional investors, $2.45trn in all.
State Street launched the first US exchange-traded fund in 1993, but, according to Bloomberg, the firm lost the top spot in US ETFs to iShares, now a unit of BlackRock, in 2003, and this year was also overtaken by Vanguard.
Fidelity launched 10 equity ETFs in 2013 while O'Hanlon was running asset management there.
Before Fidelity, O'Hanlon held top positions at Mellon Bank and Bank of New York Mellon.