They replace Matthew Savino, who is now head of alternatives sourcing at BlackRock.
Mr. Spielman is based in New York, and Mr. Cook is based in London. They will both report to Tarek Mahmoud, head of BlackRock's trading and liquidity strategies group.
Messrs. Spielman and Cook have been members of the firm's global capital markets team for the past five years. Mr. Spielman has been head of U.S. equity syndicate and capital markets, and Mr. Cook has been head of global capital markets Europe, the Middle East and Africa.
They will continue to oversee their current responsibilities in addition to their new responsibilities co-running global capital markets.