John Edward (The Cannon) Lannan (born September 27, 1984 in Long Beach, New York) is a left-handed Major League Baseball starting pitcher for the Washington Nationals.

Following his time as captain of the Chaminade High School baseball team, Lannan was selected by the Washington Nationals out of Siena College in the 11th round (324th overall) of the 2005 Major League Baseball draft.

He pitched for the low Single-A Vermont Expos in 2005 and the Single-A Savannah Sand Gnats in 2006, compiling ERA's of 5.26 and 4.76 respectively. In 2007, however, he blazed through the minors. He began the year for the high-A Potomac Nationals going 6-0 with an ERA of 2.13 and was promoted to the Double-A Harrisburg. He went 3–2 with a 3.25 ERA and got bumped up to Triple-A Columbus, where he started six games, and went 3–1 with a 1.75 ERA—and all of this before July ended.