A groundball specialist, Harrell was claimed off of waivers from the White Sox in July 2011, and turned heads with a 2012 season that saw him put up 2.6 fWAR while going 11-11 with a 3.76 ERA. Entering the 2013 season, he was viewed as a potential trade piece for the Astros, but as the season progressed, he became better known for his dislike of the defensive shifts behind him. Perhaps in an effort to avoid putting the ball in play as a result, he became increasingly fine on the mound, and saw a steadily-rising walk rate as a result.
Through three appearances in 2014, Harrell allowed as many walks - nine - as he had strikeouts. He was designated for assignment in mid-April, and subsequently assigned to Triple-A Oklahoma City.
He will begin his tenure in the Diamondbacks system at Triple-A Reno.