William O'Brien is a securities exchange executive who was appointed in April 2016 as executive chairman of Direct Match, a startup that plans to offer exchange-style trading for U.S. Treasury bonds in 2016. He leads the board of directors and will help develop corporate strategy and operations at the company.
O’Brien has spent most of his career at U.S. stock exchanges, including as president of Bats Global Markets, chief executive officer of Direct Edge and senior vice president at Nasdaq Inc.  Earlier he served as vice president of NASDAQ.
O'Brien led Direct Edge from a small ATS to become third largest stock exchange in the United States. After merging the company with Bats, he served as president of the combined organization until he left on July 22, 2014. He joined Direct Edge as CEO in July 2007.
On April 1, 2014, O'Brien got into a heated exchange on CNBC with IEX's Brad Katsuyama when the two took part in a panel on high-speed trading related to Michael Lewis's just-released book Flash Boys. The book praises IEX and Katsuyama and criticizes high-frequency trading, saying it rigs the markets in favor of the high speed traders. Link to CNBC video During the interview O'Brien told Lewis and Katsuyama "Shame on both of you!" Later that week, BATS was forced to correct something O’Brien had said about the speed of his company’s technology systems. 
Before his appointment to Direct Edge, O'Brien was senior vice president at The Nasdaq Stock Market, having held senior management positions in Nasdaq’s New Listings and Market Data units.
O'Brien joined Nasdaq in 2004 by way of Brut, LLC, where he had been chief operating officer since 2002, helping lead the company through a period of significant growth and its acquisition by Nasdaq. He originally joined Brut as senior vice president and general counsel in 2000. O'Brien was an assistant general counsel at Goldman Sachs from 1998 to 2000 and at Orrick, Herrington & Sutcliff LLP from 1995 to 1998, specializing in market regulation.
In June 2010, O’Brien won the Ernst & Young Entrepreneur Of The Year 2010 Award in the financial services category in New Jersey. 
The IEX Argument
On April 1, 2014, subsequent to the release of Michael Lewis' book Flash Boys, O'Brien, then president of Bats, and IEX CEO Brad Katsuyama engaged in a spirited debate on CNBC that distracted trading on the floor of the New York Stock Exchange, where CNBC presents its live broadcast. The above video shows the highlights of the debate.
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