[1] He was the sole owner of the Boston Red Sox of Major League Baseball for most of the 1914 through 1916 seasons, during which the team won two World Series.

He soon learned about real estate and the commodities market by listening to conversations of the wealthy patrons at his hotel and taking advice from those who were willing to share their insights with him.

On December 21, 1913, Lannin and a group of investors purchased 50% of the Boston Red Sox baseball team from Jimmy McAleer and Robert B. McRoy.

With the profit made from the sale of his team, he continued to invest in real estate ventures all around Boston and across New York State.

Lannin acquired Roosevelt Airfield on Long Island, where Charles Lindbergh began his historic transatlantic flight.