Petitti was appointed last week by Major League Baseball to succeed Rob Manfred as chief operating officer. Manfred replaces Bud Selig as commissioner on Jan, 25.
McGlarry, 46, worked for MLB from 2003-08 and was vice-president of broadcasting business affairs. He shifted to the MLB Network when it launched in 2009 as senior vice-president of programming and business affairs and then as executive vice-president of content.
He will report to Bob Bowman, who last week was appointed MLB's president of business and media. Bowman had been president of MLB Advanced Media.