Tillman was drafted by the Seattle Mariners in the second round of the 2006 Major League Baseball Draft. On February 9, 2008, Tillman, along with Adam Jones, George Sherrill, Kam Mickolio, and Tony Butler, was traded to the Baltimore Orioles for Érik Bédard. According to Baseball America, he was Baltimore's second best prospect, behind only Matt Wieters.

This Baltimore Orioles jersey was worn by Tillman during a Spring Training game in 2008. It was signed on both the front and back by Tillman and inscribed "Game Used 08."