Willis, or "D-Train," was originally selected by the Chicago Cubs in the eighth round of the 2000 amateur draft. He joined the Marlins system as a minor leaguer when Chicago traded him along with Jose Cueto, Ryan Jorgensen and Julian Tavares for Antonio Alfonseca and Matt Clement before the 2002 season.
He joined Florida in 2003, making the All-Star team and winning the NL Rookie-of-the-Year award by posting a 14-6 record and a 3.30 ERA in 27 starts. He struck out eight batters per nine innings pitched and collected a 1.282 WHIP.
After a Sophomore slump saw him post a 10-11 record with an ERA over four in 2004, Willis rebounded in 2005, making his second All-Star team and finishing second in the year ending NL Cy Young award voting. He lead the NL with 22 wins against 10 losses and a 2.63 ERA. He also led the NL with seven complete games and five shutouts.
Willis continued to be a part of the Florida rotation through 2007. After the season ended, he was traded along with Miguel Cabrera to the Detroit Tigers for Dallas Trahern, Burke Badenhop, Eulogio De La Cruz, Cameron Maybin, Andrew Miller and Mike Rabelo.
In total, Willis compiled a 68-54 record in 162 starts over five seasons with the Marlins, and is Florida's career leader in the win column. He struck out 757 in 1,022.2 innings and posted a 3.78 ERA.
Willis has since played for the Detroit Tigers, the Arizona Diamondbacks and the Cincinnati Reds. He has not enjoyed the same level of success he saw with Florida, posting a 4-15 record over four seasons.