Mitchell attended Heritage High School in Conyers, Georgia, and was a starting pitcher and third baseman from 1994-1997. Threw a no-hitter in the 1995 Mickey Mantle State Tournament. During the 1996 season he compiled a .428 batting average with 12 home runs. In 1997 his team won the 4-AAA Regional Championship. That season he posted a 7-4 record with a 1.24 ERA and 90 strikeouts over 65 innings, while batting .371 with 6 home runs, 32 RBI, and 21 stolen bases. He improved on those numbers during the summer American Legion season by batting .431 with 11 home runs and 46 RBI, while compiling a 5-0 record with a 1.10 ERA on the mound. Andy played for Team Georgia in the summer of 1997 at the Sunbelt Classic, where he made the all-tournament team....Named as an all-area selection....Graduated with honors.
Mitchell attended Georgia Tech on an athletic scholarship from 1998-2001, where he saw time as a relief pitcher and third baseman. Mitchell's time was cut short at third base with the arrival of Mark Teixeira, but he had his best year as a Yellow Jacket in 2000, when he became the short relief specialist for the team with five saves and a perfect 4-0 record. He threw five scoreless innings in the ACC Tournament, and was on the mound when they won the title game against Clemson. Andy graduated with a degree in business management in 2001.
Since signing with the Orioles organization in 2001, Andy has pitched 656 innings, with a career record of 46-27 and a 3.58 Earned Run Average. He has played for the Delmarva Shorebirds (2002), Frederick Keys (2003), Bowie Baysox (2004), Ottawa Lynx (2005-2006) and Norfolk Tides (2007-2008). Most of his work has been as a middle reliever, but in the second half of the 2007 season he had success as a starting pitcher with the Tides. After the completion of the 2007 season, Mitchell completed a championship season with the Águilas Cibaeñas in the Dominican Winter Baseball League. Andy wrapped up the 2008 season with a 12-8 record as the leader in wins for the Tides, and was 6th in wins in the International League.