Conroy replaced Thomas Balk, who stepped down at the end of last year from Fidelity Worldwide, which manages around $300 billion in assets. Fidelity Worldwide is the financial services business of FIL Limited, which is a separate company from U.S.-based Fidelity Investments, and does not operate in North America. Both companies are private.

Thomas Tesauro, head of Fidelity's prime brokerage services, has taken on the role of interim president of Fidelity Capital Markets, which is the institutional trading arm of Boston-based Fidelity Investments, while the company searches for a permanent replacement for Conroy.

Conroy, who was a regular representative for Fidelity at market structure conferences in the United States, has relocated to London from Boston for the job. He reports to Abigail Johnson, who is chairwoman of FIL and is also chief executive officer of Fidelity Investments.

(This story corrects name to Conroy from Conway in second and fourth paragraphs)

(Reporting by John McCrank; Editing by Lisa Shumaker)

By John McCrank